improve: port common code to C

This commit ports even more C++ code to C99, now, the codes available in the "common" folder.

loader/src/include/misc.h

@@ -0,0 +1,17 @@
+#ifndef MISC_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/*
+ * Bionic's atoi runs through strtol().
+ * Use our own implementation for faster conversion.
+ */
+int parse_int(const char *str);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* MISC_H */