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_WARNINGS_H__
#define __LDC_GEN_WARNINGS_H__

void warnInvalidPrintfCall(Loc loc, Expression* arguments, size_t nargs);

#endif // __LDC_GEN_WARNINGS_H__