...(presumably due to it using -fvisibility-ms-compat, cf.
solenv/gbuild/platform/com_GCC_defs.mk), or else things start to fail like
<https://ci.libreoffice.org/job/lo_ubsan/962/console>'s
CustomTarget_testtools/uno_test:

> /cpputools/source/unoexe/unoexe.cxx:502:24: runtime error: member call on address 0x60600000c288 which does not point to an object of type 'com::sun::star::lang::XMain'
> 0x60600000c260: note: object is base class subobject at offset 40 within object of type 'bridge_test::TestBridgeImpl'
>     #0 0x50dc0b in sal_main() /cpputools/source/unoexe/unoexe.cxx:502:24
>     #1 0x507762 in main /cpputools/source/unoexe/unoexe.cxx:348:1
>     #2 0x2b2ede591444 in __libc_start_main (/lib64/libc.so.6+0x22444)
>     #3 0x429425 in _start (/instdir/program/uno.bin+0x429425)

Change-Id: I7f2c38ef2f3cedae07d71246980ad1f21220db72