Runtime/math matches; better libc headers

Former-commit-id: bef7db1748

libc/string.h

@@ -0,0 +1,24 @@
+#ifndef _STRING_H_
+#define _STRING_H_
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void* memcpy(void* dest, const void* src, size_t num);
+void* memset(void* dest, int ch, size_t count);
+
+size_t strlen(const char* s);
+char* strcpy(char* dest, const char* src);
+char* strncpy(char* dest, const char* src, size_t num);
+int strcmp(const char* s1, const char* s2);
+int strncmp(const char* s1, const char* s2, size_t n);
+char* strncat(char* dest, const char* src, size_t n);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif