[PATCH] Simplify and improve x86/amd64 CPU build flags

[fabio]

The attached patch does the following:

• on amd64 removes the "-msse" flag, which is already enabled by default;
• on x86 changes the flags from "-march=i686 -msse" to "-march=pentium3 -mtune=generic". This should also enable other CPU features like MMX, while keeping the same minimun supported CPU (Intel Pentium3 or AMD Athlon 4) previously required by "-msse".

Tested on x86 (Core2 Duo).

[fabio]

actual patch

[fabio]

Better to postpone this after a new release.

[Josh]

It should be fine to commit this as soon as the Alpha 16 freeze is over.

[fabio]

In 15170:

Simplify and improve x86/amd64 CPU build flag

On amd64 removes the "-msse" flag, which is already
enabled by default.

On x86 changes the flags from "-march=i686 -msse" to
"-march=pentium3 -mtune=generic". This should also enable
other CPU features like MMX, while keeping the same
minimun supported CPU (Intel Pentium3 or AMD Athlon 4)
previously required by "-msse".

Fixes #2329.

[Raymond]

Any performance improvements? Why not: "‘core2’ Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support." ? Maybe "SSE2, SSE3 and SSSE" (in core2) improve the performance? (​https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/i386-and-x86-64-Options.html#i386-and-x86-64-Options)

Pentium III last produced until 2002. Note: SSE II support: 99 %; SSE III support: 95% (​http://feedback.wildfiregames.com/static/cpucaps.html)

So increasing the requirements to Core2Duo CPU is not a problem.

[fabio]

See discussion on forum: http://www.wildfiregames.com/forum/index.php?showtopic=18672