Make it actually work to build GLEW for debugging

The check in the GLEW Makefile looked at the whole $(MAKECMDGOALS),
which in our case was the string 'glew.lib debug', not just 'debug'.

Change-Id: I639395c944e8f2b443cbb55b451a4036b2c9d3bb
diff --git a/external/glew/UnpackedTarball_glew.mk b/external/glew/UnpackedTarball_glew.mk
index 1b100bc..64cbc5c 100644
--- a/external/glew/UnpackedTarball_glew.mk
+++ b/external/glew/UnpackedTarball_glew.mk
@@ -48,4 +48,8 @@ $(eval $(call gb_UnpackedTarball_add_patches,glew,\
))
endif

$(eval $(call gb_UnpackedTarball_add_patches,glew,\
	external/glew/glew-debug.patch.1 \
))

# vim: set noet sw=4 ts=4:
diff --git a/external/glew/glew-debug.patch.1 b/external/glew/glew-debug.patch.1
new file mode 100644
index 0000000..c6e30a4
--- /dev/null
+++ b/external/glew/glew-debug.patch.1
@@ -0,0 +1,12 @@
-*- Mode: Diff -*-
--- glew/Makefile
+++ glew/Makefile
@@ -65,7 +65,7 @@
 RM      ?= rm -f
 LN      ?= ln -sf
 
-ifeq ($(MAKECMDGOALS), debug)
+ifneq (,$(filter debug,$(MAKECMDGOALS)))
 OPT = -g
 else
 OPT = $(POPT)