https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78136
James Greenhalgh <jgreenhalgh at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2016-10-28 CC| |jgreenhalgh at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #1 from James Greenhalgh <jgreenhalgh at gcc dot gnu.org> --- Confirmed. The glibc patch that causes this is: https://sourceware.org/ml/libc-alpha/2016-10/msg00240.html And the particular hunk that introduces the problem to stdlib.h is: +/* Convert a floating-point number to a string. */ +#if __GLIBC_USE (IEC_60559_BFP_EXT) Where __GLIBC_USE is defined as: #define __GLIBC_USE(F) __GLIBC_USE_ ## F Which fails when CPP is in "traditional" mode.