Merge bitcoin-core/secp256k1#1333: test: Warn if both VERIFY and COVERAGE are defined

e83801f test: Warn if both `VERIFY` and `COVERAGE` are defined (Hennadii Stepanov)

Pull request description:

  Solves one item in bitcoin-core/secp256k1#1235.

  Also see: bitcoin-core/secp256k1#1113 (comment).

ACKs for top commit:
  sipa:
    utACK e83801f
  real-or-random:
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Tree-SHA512: 25e10a09ba2c3585148becd06f2a03d85306208bda333827c9ba73eb7fd94ad15536f10daf1b335703e5cb0539584f001501ce9c578f478ff1ebc1051aefde7d

Author: real-or-random

src/tests.c

@@ -14,6 +14,9 @@
     #pragma message("Ignoring USE_EXTERNAL_CALLBACKS in tests.")
     #undef USE_EXTERNAL_DEFAULT_CALLBACKS
 #endif
+#if defined(VERIFY) && defined(COVERAGE)
+    #pragma message("Defining VERIFY for tests being built for coverage analysis support is meaningless.")
+#endif
 #include "secp256k1.c"
 
 #include "../include/secp256k1.h"