ARC: Override toplevel default -O2 with -O3

ARC kernels have historically been built with -O3, despite top level
Makefile defaulting to -O2. This was facilitated by implicitly ordering
of arch makefile include AFTER top level assigned -O2.

An upstream fix to top level a1c48bb ("Makefile: Fix unrecognized
cross-compiler command line options") changed the ordering, making ARC
-O3 defunt.

Fix that by NOT relying on any ordering whatsoever and use the right
mechanism to do the over-rides.

Suggested-by: Michal Marek <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>

Author: vineetgarc

arch/arc/Makefile

@@ -50,6 +50,7 @@ endif
 ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
 # Generic build system uses -O2, we want -O3
 cflags-y  += -O3
+KCFLAGS += -O3
 endif
 
 # small data is default for elf32 tool-chain. If not usable, disable it