Yes, it looks similar. I went on to build FFmpeg with 10.3.0 so overwrote my trp.
As for SeaMonkey and 10.3.0, I found this in the log,
32:51.04 Y:/work/cc45-git/mozilla/gfx/thebes/gfxFont.h: In constructor 'gfxShapedWord::gfxShapedWord(const uint8_t*, uint32_t, int32_t, int32_t, uint32_t)':
32:51.04 Y:/work/cc45-git/mozilla/gfx/thebes/gfxFont.h:1277:72: warning: 'void*memset(void*, int, size_t)' clearing an object of non-trivial type 'class gfxShapedText::CompressedGlyph'; use assignment or value-initialization instead [-Wclass-memaccess]
So I added -Wclass-memaccess to CXXFLAGS (actually the optimize parameter) and that fixed the missing symbol.
Now the compile dies while linking xul.dll with a Python OSError (Errno 22), which I believe is a failure to pass the list file to emxomfld. We're linking over a 1000 object files.
Had the same or similar problem with GCC 9.2.0 and I worked around by creating my own list(response) file and manually calling emxomfld until Dmitriy fixed it sometime later.
IIRC, the problem with 9.2.0 was actually nested response files and was one of the last fixes for 9.2.0