contrib: glew: drop debug postfix from the library name

With 4d57652c the Cmake BUILD_TYPE is
set to Debug when optimizations are disabled, which is then used by glew
to determine the resulting library name.

This in turn confuses our build of projectM, which uses glew32 as a name
to use when linking.

contrib/src/glew/glew-drop-debug-postfix.patch

+--- glew.pristine/build/cmake/CMakeLists.txt	2017-07-31 14:25:39.000000000 +0300
++++ glew/build/cmake/CMakeLists.txt	2019-10-27 06:26:55.413590264 +0300
+@@ -13,8 +13,6 @@
+   cmake_policy (SET CMP0042 NEW)
+ endif()
+ 
+-set(CMAKE_DEBUG_POSTFIX d)
+-
+ option (BUILD_UTILS "utilities" ON)
+ option (GLEW_REGAL "Regal mode" OFF)
+ option (GLEW_OSMESA "OSMesa mode" OFF)

contrib/src/glew/rules.mak

@@ -13,6 +13,7 @@ $(TARBALLS)/glew-$(GLEW_VERSION).tgz:
 
 glew: glew-$(GLEW_VERSION).tgz .sum-glew
 	$(UNPACK)
+	$(APPLY) $(SRC)/glew/glew-drop-debug-postfix.patch
 	$(MOVE)
 
 .glew: glew toolchain.cmake