expr is now cast to void in THROWS family of assertions.

This prevents Clang from complaining about unused value in expressions
containing explicit casts used in the THROW assertion macro family.

Example:
`REQUIRE_THROWS_AS(static_cast<bool>(object), std::bad_cast);` would
trigger `-Wunused-value` warning. Now it does not.

Credits to Arto Bendiken, who submitted a PR almost 3 years ago, but his
branch has since died and I was unable to merge it.

include/internal/catch_capture.hpp

@@ -58,7 +58,7 @@
     do { \
         Catch::ResultBuilder __catchResult( macroName, CATCH_INTERNAL_LINEINFO, #expr, resultDisposition ); \
         try { \
-            expr; \
+            static_cast<void>(expr); \
             __catchResult.captureResult( Catch::ResultWas::Ok ); \
         } \
         catch( ... ) { \
@@ -73,7 +73,7 @@
         Catch::ResultBuilder __catchResult( macroName, CATCH_INTERNAL_LINEINFO, #expr, resultDisposition, #matcher ); \
         if( __catchResult.allowThrows() ) \
             try { \
-                expr; \
+                static_cast<void>(expr); \
                 __catchResult.captureResult( Catch::ResultWas::DidntThrowException ); \
             } \
             catch( ... ) { \
@@ -90,7 +90,7 @@
         Catch::ResultBuilder __catchResult( macroName, CATCH_INTERNAL_LINEINFO, #expr, resultDisposition ); \
         if( __catchResult.allowThrows() ) \
             try { \
-                expr; \
+                static_cast<void>(expr); \
                 __catchResult.captureResult( Catch::ResultWas::DidntThrowException ); \
             } \
             catch( exceptionType ) { \