Add an 'optinfo' build target

The 'optinfo' build target asks GCC to print optimizations that
could not be performed to local 'missing.txt' files; these will
appear in each repsective subdirectory having source files.

Both GCC and Clang will now print Verbose vectorization information
during the build process, often describing why vectorization
cannot be performed.

This commit also enables basic instruction and math vectorization
for both the 'release' and 'optinfo' targets. This includes making
use of altivec instructions (available on all powerpc processors),
and at a minimum sse4.2 on all x86_64 processors (circa-2008+ AMD
and Intel CPUs).

Vectorization is also re-enabled for GCC FDO builds, which would
otherwise be disabled when we switch to -O2 optimizations.

.gitignore

@@ -58,6 +58,7 @@ make.log
 .previous_build
 .current_build
 *.defines
+missed.txt
 
 # Visual Studio
 .vs