user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/internal/generic/global-config.cpp

@@ -0,0 +1,27 @@
+#include <stdlib.h>
+#include <string.h>
+#include <mlibc/global-config.hpp>
+
+namespace mlibc {
+
+struct GlobalConfigGuard {
+	GlobalConfigGuard();
+};
+
+GlobalConfigGuard guard;
+
+GlobalConfigGuard::GlobalConfigGuard() {
+	// Force the config to be created during initialization of libc.so.
+	mlibc::globalConfig();
+}
+
+static bool envEnabled(const char *env) {
+	auto value = getenv(env);
+	return value && *value && *value != '0';
+}
+
+GlobalConfig::GlobalConfig() {
+	debugMalloc = envEnabled("MLIBC_DEBUG_MALLOC");
+}
+
+} // namespace mlibc