Merge bitcoin-core/secp256k1#1274: test: Silent noisy clang warnings about Valgrind code on macOS x86_64

747ada3 test: Silent noisy clang warnings about Valgrind code on macOS x86_64 (Hennadii Stepanov)

Pull request description:

  Since bitcoin#1206, on macOS x86_64 with Valgrind installed, clang emits a massive amount of `-Wreserved-identifier` and `-Wreserved-macro-identifier` warnings from the `valgrind/valgrind.h` and `valgrind/memcheck.h` headers.

  This PR prevents warnings emitted for the Valgrind code.

ACKs for top commit:
  real-or-random:
    utACK 747ada3

Tree-SHA512: dd1b2b9db2d471939fdc30f9d8fd106a12f21ec5008ca98d8ebe3087d7ea352d564e8bbd0cec59a004e084af3a84d4680cb81f2ef6fe13cf164b7691e33f437d

Author: real-or-random

src/checkmem.h

@@ -58,7 +58,14 @@
 #if !defined SECP256K1_CHECKMEM_ENABLED
 #  if defined VALGRIND
 #    include <stddef.h>
+#  if defined(__clang__) && defined(__APPLE__)
+#    pragma clang diagnostic push
+#    pragma clang diagnostic ignored "-Wreserved-identifier"
+#  endif
 #    include <valgrind/memcheck.h>
+#  if defined(__clang__) && defined(__APPLE__)
+#    pragma clang diagnostic pop
+#  endif
 #    define SECP256K1_CHECKMEM_ENABLED 1
 #    define SECP256K1_CHECKMEM_UNDEFINE(p, len) VALGRIND_MAKE_MEM_UNDEFINED((p), (len))
 #    define SECP256K1_CHECKMEM_DEFINE(p, len) VALGRIND_MAKE_MEM_DEFINED((p), (len))