Refactor: moves memrchr to global impl for potential future use

src/common/impl/memrchr.c

@@ -0,0 +1,19 @@
+#include "common/memrchr.h"
+#include <stddef.h>
+#include <stdint.h>
+
+void* memrchr(const void* s, int c, size_t n)
+{
+    if (n == 0) return NULL;
+
+    const uint8_t uc = (uint8_t) c;
+
+    const uint8_t* p = (const uint8_t*) s + n;
+
+    while (n--)
+    {
+        if (*--p == uc) return (void*) p;
+    }
+
+    return NULL;
+}

src/common/memrchr.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// `memrchr` is a GNU extension and may not be declared by system headers even when the symbol exists.
+// Declare it unconditionally; the build system provides a fallback implementation when missing.
+void* memrchr(const void* s, int c, size_t n);
+
+#ifdef __cplusplus
+}
+#endif

src/common/solaris/memrchr.c

@@ -1,15 +0,0 @@
-#if defined(__sun) && ! defined(__illumos__)
-#include "memrchr.h"
-
-void *memrchr(const void *s, int c, size_t n)
-{
-    if(n == 0) return NULL;
-    const unsigned char *p = (const unsigned char *)s + n;
-    while (n--) {
-        if (*(--p) == (unsigned char) c)
-            return (void*) p;
-    }
-
-    return NULL;
-}
-#endif

src/common/solaris/memrchr.h

@@ -1,6 +0,0 @@
-#pragma once
-#include <stddef.h>
-
-#if defined(__sun) && !defined(__illumos__)
-void *memrchr(const void *s, int c, size_t n);
-#endif