lib/string: change return types to match C standard

The return type of strspn and strcspn is supposed to be a size_t and not
a signed integer.

TEST=Now the openSIL code can be built with the coreboot headers without
needing to add '-Wno-builtin-declaration-mismatch' or
'-Wno-incompatible-library-redeclaration' to the cflags. Before the
build would error out with various 'mismatch in return type of built-in
function' errors.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I0ff612e2eee4f556f5c572b02cbc600ca411ae20
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83223
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/include/string.h

@@ -20,8 +20,8 @@ char *strncpy(char *to, const char *from, size_t count);
 char *strcpy(char *dst, const char *src);
 int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, size_t maxlen);
-int strspn(const char *str, const char *spn);
-int strcspn(const char *str, const char *spn);
+size_t strspn(const char *str, const char *spn);
+size_t strcspn(const char *str, const char *spn);
 char *strstr(const char *haystack, const char *needle);
 char *strtok_r(char *str, const char *delim, char **ptr);
 char *strtok(char *str, const char *delim);

src/lib/string.c

@@ -125,9 +125,9 @@ int strncmp(const char *s1, const char *s2, size_t maxlen)
 	return 0;
 }
 
-int strspn(const char *str, const char *spn)
+size_t strspn(const char *str, const char *spn)
 {
-	int ret = 0;
+	size_t ret = 0;
 
 	while (*str != 0) {
 		const char *p;
@@ -140,9 +140,9 @@ int strspn(const char *str, const char *spn)
 	return ret;
 }
 
-int strcspn(const char *str, const char *spn)
+size_t strcspn(const char *str, const char *spn)
 {
-	int ret = 0;
+	size_t ret = 0;
 
 	while (*str != 0) {
 		const char *p;