user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/posix/regex.c

@@ -0,0 +1,30 @@
+#include <regex.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+ 
+int main(void) {
+	char *testString = "mlibc is the best best best libc";
+	char *pattern = "\\(be[a-z]t\\) \\1";
+
+	regex_t reg;
+	int rc = regcomp(&reg, pattern, 0);
+	assert(!rc);
+
+	regmatch_t matches[2];
+	rc = regexec(&reg, testString, 2, matches, 0);
+	assert(!rc);
+
+	printf("Whole pattern: \"%.*s\" at %zd-%zd.\n",
+		(int)(matches[0].rm_eo - matches[0].rm_so), &testString[matches[0].rm_so],
+		(ssize_t)matches[0].rm_so, (ssize_t)(matches[0].rm_eo - 1));
+	assert(matches[0].rm_so == 13 && matches[0].rm_eo == 22);
+
+	printf("Substring: \"%.*s\" at %zd-%zd.\n",
+		(int)(matches[1].rm_eo - matches[1].rm_so), &testString[matches[1].rm_so],
+		(ssize_t)matches[1].rm_so, (ssize_t)matches[1].rm_eo - 1);
+	assert(matches[1].rm_so == 13 && matches[1].rm_eo == 17);
+
+	regfree(&reg);
+	return 0;
+}