Fixed DStress tests nocompile/c/{const_32_B.d,const_32_C.d}. Updated the runtest script to build libtangobos-partial.a if it hasn't already been built. Added in signbit() and va_arg!()() to libtangobos-partial.a so more of the phobos dependent DStress tests pass.

#ifndef LDC_GEN_PROGRAMS_H
#define LDC_GEN_PROGRAMS_H

#include "llvm/System/Path.h"

llvm::sys::Path getGcc();

#endif