qtwebengine-5.12.0 fails to build on arm

qtwebengine-5.12.0 fails to build on  arch with error:

[7/172] CXX base/json/json_parser.o
FAILED: base/json/json_parser.o
c++ -MMD -MF base/json/json_parser.o.d -I/builddir/build/BUILD/qtwebengine-everywhere-src-5.12.0/src/3rdparty/gn -I/builddir/build/BUILD/qtwebengine-everywhere-src-5.12.0/src/3rdparty/gn/out/Release -DNDEBUG -O3 -fdata-sections -ffunction-sections -D_FILE_OFFSET_BITS=64 -D_STDC_CONSTANT_MACROS -D_STDC_FORMAT_MACROS -pthread -pipe -fno-exceptions -fno-rtti -std=c+14 -Wno-c+11-narrowing -c /builddir/build/BUILD/qtwebengine-everywhere-src-5.12.0/src/3rdparty/gn/base/json/json_parser.cc -o base/json/json_parser.o
In file included from /builddir/build/BUILD/qtwebengine-everywhere-src-5.12.0/src/3rdparty/gn/base/json/json_parser.cc:13:
/builddir/build/BUILD/qtwebengine-everywhere-src-5.12.0/src/3rdparty/gn/base/numerics/safe_conversions.h:17:10: fatal error: base/numerics/safe_conversions_arm_impl.h: No such file or directory
#include "base/numerics/safe_conversions_arm_impl.h"
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

maybe just an include path issue, as I do see a copy of the aforementioned file at:

./src/3rdparty/chromium/base/numerics/safe_conversions_arm_impl.h