Enable the inlinehint attribute in the Inliner.

Functions explicitly marked inline will get an inlining threshold slightly
more aggressive than the default for -O3. This means than -O3 builds are
mostly unaffected while -Os builds will be a bit bigger and faster.

The difference depends entirely on how many 'inline's are sprinkled on the
source.

In the CINT2006 suite, only these tests are significantly affected under -Os:

               Size   Time
471.omnetpp   +1.63% -1.85%
473.astar     +4.01% -6.02%
483.xalancbmk +4.60%  0.00%

Note that 483.xalancbmk runs too quickly to give useful timing results.

llvm-svn: 96066