perf tools: Add 'make DEBUG=1' to remove the -O6 cflag

commit 60d526f7 upstream.

When using gdb to debug perf, it is practically impossible to
use when perf is compiled with -O6. For developers, this patch
adds the DEBUG feature to the make command line so that a
developer can easily remove the optimization flag.

LKML-Reference: <1255590330.8392.446.camel@twins>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20091020232033.984323261@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
[bwh: Backport to 2.6.32]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

tools/perf/Makefile

@@ -200,7 +200,14 @@ EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wold-style-definition
 EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wstrict-prototypes
 EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wdeclaration-after-statement
 
-CFLAGS = $(MBITS) -ggdb3 -Wall -Wextra -std=gnu99 -Werror -O6 -fstack-protector-all -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS)
+ifeq ("$(origin DEBUG)", "command line")
+  PERF_DEBUG = $(DEBUG)
+endif
+ifndef PERF_DEBUG
+  CFLAGS_OPTIMIZE = -O6
+endif
+
+CFLAGS = $(MBITS) -ggdb3 -Wall -Wextra -std=gnu99 -Werror $(CFLAGS_OPTIMIZE) -fstack-protector-all -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS)
 LDFLAGS = -lpthread -lrt -lelf -lm
 ALL_CFLAGS = $(CFLAGS)
 ALL_LDFLAGS = $(LDFLAGS)