musl: make strtoll() accept strings start with dot

glibc accepts strings start with '.' and returns 0, but musl refuses
them. Let's accept them, as our code assumes the function accept such
strings.

src/include/musl/stdlib.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include_next <stdlib.h>
+
+long long strtoll_fallback(const char *nptr, char **endptr, int base);
+#define strtoll strtoll_fallback

src/libc/musl/meson.build

@@ -6,5 +6,6 @@ endif
 
 libc_wrapper_sources += files(
         'stdio.c',
+        'stdlib.c',
         'string.c',
 )

src/libc/musl/stdlib.c

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <stdlib.h>
+
+/* The header stdlib.h overrides strtoll with strtoll_fallback, hence we need to undef it here. */
+#undef strtoll
+
+long long strtoll_fallback(const char *nptr, char **endptr, int base) {
+        /* glibc returns 0 if the first character is '.' without error, but musl returns as an error.
+         * As our code assumes the glibc behavior, let's accept strings start with '.'. */
+        if (nptr && *nptr == '.') {
+                if (endptr)
+                        *endptr = (char*) nptr;
+                return 0;
+        }
+
+        /* Otherwise, use the native strtoll(). */
+        return strtoll(nptr, endptr, base);
+}