Added missing file mutex.h

avm2_env/usr/include/machine/mutex.h
Fixed unresolved symbols of long double version functions.

Such as atanl, rintl and etc.
Made a little changes in Makefile. And by default no gcc built.

Now gcc and gcclibs are not going to be built. Only llvm-3.2.
Some minor changes for easy using.
Experimental va_arg support