Add -DNDEBUG to std_cmake_args

CMake has -DNDEBUG and -O3 as its default flags for Release builds.
Homebrew clears out the default CMake flags, which is fine for
optimization because Homebrew passes its own optimization flag(s).
-DNDEBUG wasn't added back in, though.

This ensures -DNDEBUG is passed to CMake release builds by default,
instead of individual formulas having to add it explicitly.

This also removes explicit additions of -DNDEBUG from the formulae that
had them -- gflags, llvm, and taglib.

Closes Homebrew/homebrew#47378.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/formula.rb

@@ -1041,8 +1041,8 @@ class Formula
   # less consistent and the standard parameters are more memorable.
   def std_cmake_args
     %W[
-      -DCMAKE_C_FLAGS_RELEASE=
-      -DCMAKE_CXX_FLAGS_RELEASE=
+      -DCMAKE_C_FLAGS_RELEASE=-DNDEBUG
+      -DCMAKE_CXX_FLAGS_RELEASE=-DNDEBUG
       -DCMAKE_INSTALL_PREFIX=#{prefix}
       -DCMAKE_BUILD_TYPE=Release
       -DCMAKE_FIND_FRAMEWORK=LAST