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 _GNUC_H
#define _GNUC_H 1

int memicmp(const char *s1, const char *s2, int n);
int stricmp(const char *s1, const char *s2);

#endif