libroot: Replace getsubopt implementation with musl's.

It looks to be a bit more optimized, and one less thing for
us to have to maintain from POSIX.

src/system/libroot/posix/musl/misc/Jamfile

@@ -12,6 +12,7 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 		MergeObject <$(architecture)>posix_musl_misc.o :
 			a64l.c
 			ffs.c
+			getsubopt.c
 			;
 	}
 }

src/system/libroot/posix/musl/misc/getsubopt.c

@@ -0,0 +1,23 @@
+#include <stdlib.h>
+#include <string.h>
+
+int getsubopt(char **opt, char *const *keys, char **val)
+{
+	char *s = *opt;
+	int i;
+
+	*val = NULL;
+	*opt = strchr(s, ',');
+	if (*opt) *(*opt)++ = 0;
+	else *opt = s + strlen(s);
+
+	for (i=0; keys[i]; i++) {
+		size_t l = strlen(keys[i]);
+		if (strncmp(keys[i], s, l)) continue;
+		if (s[l] == '=')
+			*val = s + l + 1;
+		else if (s[l]) continue;
+		return i;
+	}
+	return -1;
+}

src/system/libroot/posix/stdlib/Jamfile

@@ -21,7 +21,6 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			div.c
 			env.cpp
 			exit.cpp
-			getsubopt.cpp
 			heapsort.c
 			merge.c
 			mktemp.c

src/system/libroot/posix/stdlib/getsubopt.cpp

@@ -1,39 +0,0 @@
-/*
- * Copyright 2010, Oliver Tappe <zooey@hirschkaefer.de>.
- * Distributed under the terms of the MIT License.
- */
-
-
-#include <stdlib.h>
-#include <string.h>
-
-
-int
-getsubopt(char** optionPtr, char* const* keys, char** valuePtr)
-{
-	if (optionPtr == NULL || valuePtr == NULL)
-		return -1;
-
-	char* option = *optionPtr;
-	if (*option == '\0')
-		return -1;
-
-	char* startOfNextOption = strchr(option, ',');
-	if (startOfNextOption != NULL)
-		*startOfNextOption++ = '\0';
-	else
-		startOfNextOption = option + strlen(option);
-	*optionPtr = startOfNextOption;
-
-	char* startOfValue = strchr(option, '=');
-	if (startOfValue != NULL)
-		*startOfValue++ = '\0';
-	*valuePtr = startOfValue;
-
-	for (int keyIndex = 0; keys[keyIndex] != NULL; ++keyIndex) {
-		if (strcmp(option, keys[keyIndex]) == 0)
-			return keyIndex;
-	}
-
-	return -1;
-}