math: raise flags in log2l.c on <= 0 arguments, and fix volatile

[musl] / arch / x86_64 / bits / stdarg.h

#define va_start(v,l)   __builtin_va_start(v,l)
#define va_end(v)       __builtin_va_end(v)
#define va_arg(v,l)     __builtin_va_arg(v,l)
#define va_copy(d,s)    __builtin_va_copy(d,s)