GitLab

The commit fb25cd08 went a bit too far and removed safeseh
when -clang-cl was passed, but that's only needed in x86-64
which is already handled by the -m64 flag.

I discovered this when building Firefox x86 with clang-cl.

This is required for AddressSanitizer builds with clang-cl.

* Don't try to mix incompatible optimization flags in debug builds.
* Workaround ax_cc_maxopt.m4 not supporting MSVC and change -O3 to -O2.
* Fix MSVC warning by properly passing linker flags to compiler.
* Make msvcc.sh return 1 if invalid command line options are used rather than silently eating them.
* Add more comments.