backport MBEDTLS_MAYBE_UNUSED

Signed-off-by: Dave Rodgman <[email protected]>

library/common.h

@@ -350,4 +350,31 @@ static inline const unsigned char *mbedtls_buffer_offset_const(
 #define MBEDTLS_STATIC_ASSERT(expr, msg)
 #endif
 
+/* Suppress compiler warnings for unused functions and variables. */
+#if !defined(MBEDTLS_MAYBE_UNUSED) && defined(__has_attribute)
+#    if __has_attribute(unused)
+#        define MBEDTLS_MAYBE_UNUSED __attribute__((unused))
+#    endif
+#endif
+#if !defined(MBEDTLS_MAYBE_UNUSED) && defined(__GNUC__)
+#    define MBEDTLS_MAYBE_UNUSED __attribute__((unused))
+#endif
+#if !defined(MBEDTLS_MAYBE_UNUSED) && defined(__IAR_SYSTEMS_ICC__) && defined(__VER__)
+/* IAR does support __attribute__((unused)), but only if the -e flag (extended language support)
+ * is given; the pragma always works.
+ * Unfortunately the pragma affects the rest of the file where it is used, but this is harmless.
+ * Check for version 5.2 or later - this pragma may be supported by earlier versions, but I wasn't
+ * able to find documentation).
+ */
+#    if (__VER__ >= 5020000)
+#        define MBEDTLS_MAYBE_UNUSED _Pragma("diag_suppress=Pe177")
+#    endif
+#endif
+#if !defined(MBEDTLS_MAYBE_UNUSED) && defined(_MSC_VER)
+#    define MBEDTLS_MAYBE_UNUSED __pragma(warning(suppress:4189))
+#endif
+#if !defined(MBEDTLS_MAYBE_UNUSED)
+#    define MBEDTLS_MAYBE_UNUSED
+#endif
+
 #endif /* MBEDTLS_LIBRARY_COMMON_H */