[sanitizer_common] Restore sanitizer_procmaps_solaris.cpp compilation on Solaris 11.3

When upstream `compiler-rt` was recently imported into GCC's
`libsanitizer`, Solaris 11.3 bootstrap broke because in 11.3
`<sys/procfs.h>` doesn't mix with largefile compilation.  I'd caused this
in D129837 <https://reviews.llvm.org/D129837> where I forgot that the code
still needs to support Solaris 11.3.

Fixed by restoring the `#undef _FILE_OFFSET_BITS`.

Tested on `sparc-sun-solaris2.11` and `amd64-pc-solaris2.11` (Solaris 11.4)
in LLVM and both Solaris 11.3 and 11.4 in GCC.

Differential Revision: https://reviews.llvm.org/D133556