this is all probably very old news and probably fixed in a later OSX, but.....
on my 10.4.11 machine, math.h has (IMHO this bug)

#define HUGE_VALF 1e50f

this compiles when I build LLVM using "configure", but not with "cmake", probably
to do with different C-standard-ness and pedantic-ness switches....

I would recommend LLVM Support not import the HUGE_VAL, HUGE_VALF feature,
and instead use its own definition, I redefined HUGE_VALF in Support/DataTypes.h
{.in,.cmake} to be 3.4e38f and got LLVM to build on 10.4.11 that way.

Peter Lawrence.