dev-embedded/simulavr: fix build with modern GCC

dev-embedded/simulavr: fix build with modern GCC

The bundled googletest 1.10.0 copy under regress/gtest fails to
compile with GCC 15: gtest-death-test.cc uses uintptr_t without
including <cstdint>, which older GCC/libstdc++ used to pull in
transitively via <limits.h> but no longer does. The regress/
subdirectory is unconditionally added to the "all" target with no
CMake toggle to skip it, so this breaks a plain build, not just
`make check`. Verified by building the release-1.1.0 tag standalone
with cmake/make outside the ebuild sandbox: the fix lets both the
main build and `make doc` complete.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>