ARM-specific optimizations

Thanks to NiLuJe who pointed out that our generic -march=armv6 can be
replaced (for K2/K3/DX/DXG) with a more specific optimization:
-march=armv6j -mtune=arm1136jf-s -mfpu=vfp. This I have now done and
also passed ARM_CFLAGS value to CXXFLAGS which is then passed to
crengine build. Tested, works fine. The performance improvement is
negligible (a few ms per page, but seems to be consistently better, i.e.
not just plus/minus fluctuations).

Makefile

@@ -30,7 +30,7 @@ HOSTCXX:=g++
 CFLAGS:=-O3 $(SYSROOT)
 CXXFLAGS:=-O3 $(SYSROOT)
 LDFLAGS:= $(SYSROOT)
-ARM_CFLAGS:=-march=armv6
+ARM_CFLAGS:=-march=armv6j -mtune=arm1136jf-s -mfpu=vfp
 # use this for debugging:
 #CFLAGS:=-O0 -g
 
@@ -58,6 +58,7 @@ ifdef EMULATE_READER
 	endif
 else
 	CFLAGS+= $(ARM_CFLAGS)
+	CXXFLAGS+= $(ARM_CFLAGS)
 endif
 
 # standard includes
@@ -193,7 +194,7 @@ endif
 
 $(CRENGINELIBS):
 	cd $(KPVCRLIBDIR) && rm -rf CMakeCache.txt CMakeFiles && \
-		CFLAGS="$(CFLAGS)" CC="$(CC)" CXX="$(CXX)" cmake . && \
+		CFLAGS="$(CFLAGS)" CXXFLAGS="$(CXXFLAGS)" CC="$(CC)" CXX="$(CXX)" cmake . && \
 		make
 
 $(LUALIB):