After hours of compiling:

release/../../../../qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:145:19: warning: type ‘struct RefCountedThreadSafeBase’ violates the C++ One Definition Ru
le [-Wodr]
  145 | class BASE_EXPORT RefCountedThreadSafeBase {
      |                   ^
/usr/src/debug/qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:145:19: note: a different type is defined in another translation unit
/usr/src/debug/qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:229:16: note: the first difference of corresponding 
definitions is field ‘needs_adopt_ref_’
/usr/src/debug/qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:145:19: note: a type with different number of fields is defined in another translation unit
release/../../../../qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:387:7: warning: type ‘struct RefCountedThreadSafe’ violates the C++ One Definition Rule [-
Wodr]
  387 | class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
      |       ^
/usr/src/debug/qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:387:7: note: a type with different bases is defined in another translation unit
release/../../../../qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:387:7: warning: type ‘struct RefCountedThreadSafe’ violates the C++ One Definition Rule [-Wodr]
  387 | class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
      |       ^
/usr/src/debug/qtwebengine/src/3rdparty/chromium/base/memory/ref_counted.h:387:7: note: a type with different bases is defined in another translation unit
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:87:38: warning: type ‘struct CookieMonsterDelegateQt’ violates the C++ One Definition Rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:87:38: note: a type with different bases is defined in another translation unit
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:104:10: warning: type of ‘setCookie’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:134:6: note: ‘setCookie’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:134:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:113:10: warning: type of ‘setHasFilter’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:212:6: note: ‘setHasFilter’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:212:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:108:10: warning: type of ‘deleteAllCookies’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:183:6: note: ‘deleteAllCookies’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:183:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:107:10: warning: type of ‘deleteSessionCookies’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:171:6: note: ‘deleteSessionCookies’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:171:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:105:10: warning: type of ‘deleteCookie’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:158:6: note: ‘deleteCookie’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:158:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:106:10: warning: type of ‘getAllCookies’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:129:6: note: ‘getAllCookies’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:129:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.h:102:10: warning: type of ‘hasCookieMonster’ does not match original declaration [-Wlto-type-mismatch]
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:124:6: note: ‘hasCookieMonster’ was previously declared here
/usr/src/debug/qtwebengine/src/core/net/cookie_monster_delegate_qt.cpp:124:6: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: warning: virtual table of type ‘struct CallbackSharedDataPointer’ violates one definition rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: note: the conflicting type defined in another translation unit has virtual table with more entries
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: warning: virtual table of type ‘struct CallbackSharedDataPointer’ violates one definition rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: note: the conflicting type defined in another translation unit has virtual table with more entries
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: warning: virtual table of type ‘struct CallbackSharedDataPointer’ violates one definition rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: note: the conflicting type defined in another translation unit has virtual table with more entries
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: warning: virtual table of type ‘struct CallbackSharedDataPointer’ violates one definition rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: note: the conflicting type defined in another translation unit has virtual table with more entries
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: warning: virtual table of type ‘struct CallbackSharedDataPointer’ violates one definition rule [-Wodr]
/usr/src/debug/qtwebengine/src/core/api/qwebenginecallback_p.h:136:12: note: the conflicting type defined in another translation unit has virtual table with more entries
during RTL pass: pro_and_epilogue
release/gen/services/network/public/mojom/content_security_policy.mojom.h: In member function ‘Clone’:
release/gen/services/network/public/mojom/content_security_policy.mojom.h:1666:1: internal compiler error: in find_oldest_value_reg, at regcprop.cc:460

This is sort of unmaintainable..