musl-tcc/src/ctype/isupper.c

#include <ctype.h>
#undef isupper

int isupper(int c)
{
	return (unsigned)c-'A' < 26;
}

int __isupper_l(int c, locale_t l)
{
	return isupper(c);
}

weak_alias(__isupper_l, isupper_l);