Fix conflict between constant deprecation and check-names.sh

The previous introduction of constant deprecation macros
in platform_util.h lead to failure of tests/scrips/check-names.sh
because the regular expressions in the latter choked on the brackets
in the part `__attribute__((deprecated))` of the definition of the
helper type `mbedtls_deprecated_{numeric|string}_constant_t`.

Postponing any further study and potential robustness improvements
in check-names.sh to another time, this commit circumvents this
problem by temporarily abbreviating  `__attribute__((deprecated))`
as `MBEDTLS_DEPRECATED`, which doesn't lead to problems with
check-names.sh.
diff --git a/include/mbedtls/platform_util.h b/include/mbedtls/platform_util.h
index 9da6f0f..bdf9252 100644
--- a/include/mbedtls/platform_util.h
+++ b/include/mbedtls/platform_util.h
@@ -44,18 +44,18 @@
 /* Internal helper macros for deprecating API constants. */
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
 #if defined(MBEDTLS_DEPRECATED_WARNING)
-/* Deliberately don't (yet) define MBEDTLS_DEPRECATED here to avoid
- * conflict with other headers which define and use it, too.
- * We might want to move all these definitions here at some point
- * for uniformity. */
-__attribute__((deprecated))
-typedef char const * mbedtls_deprecated_string_constant_t;
+/* Deliberately don't (yet) export MBEDTLS_DEPRECATED here
+ * to avoid conflict with other headers which define and use
+ * it, too. We might want to move all these definitions here at
+ * some point for uniformity. */
+#define MBEDTLS_DEPRECATED __attribute__((deprecated))
+MBEDTLS_DEPRECATED typedef char const * mbedtls_deprecated_string_constant_t;
 #define MBEDTLS_DEPRECATED_STRING_CONSTANT( VAL )       \
     ( (mbedtls_deprecated_string_constant_t) ( VAL ) )
- __attribute__((deprecated))
-typedef int mbedtls_deprecated_numeric_constant_t;
+MBEDTLS_DEPRECATED typedef int mbedtls_deprecated_numeric_constant_t;
 #define MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( VAL )       \
     ( (mbedtls_deprecated_numeric_constant_t) ( VAL ) )
+#undef MBEDTLS_DEPRECATED
 #else /* MBEDTLS_DEPRECATED_WARNING */
 #define MBEDTLS_DEPRECATED_STRING_CONSTANT( VAL ) VAL
 #define MBEDTLS_DEPRECATED_NUMERIC_CONSTANT( VAL ) VAL