selftests/powerpc: Add flags.mk to support pmu buildable

When running `make -C powerpc/pmu run_tests` from top level selftests
directory, currently this error is being reported:

  make: Entering directory '/home/maddy/linux/tools/testing/selftests/powerpc/pmu'
  Makefile:40: warning: overriding recipe for target 'emit_tests'
  ../../lib.mk:111: warning: ignoring old recipe for target 'emit_tests'
  gcc -m64    count_instructions.c ../harness.c event.c lib.c ../utils.c loop.S  -o /home/maddy/selftest_output//count_instructions
  In file included from count_instructions.c:13:
  event.h:12:10: fatal error: utils.h: No such file or directory
  12 | #include "utils.h"
    |          ^~~~~~~~~
  compilation terminated.

This is due to missing of include path in CFLAGS. That is, CFLAGS and
GIT_VERSION macros are defined in the powerpc/ folder Makefile which
in this case is not involved.

To address the failure in case of executing specific sub-folder test
directly, a new rule file has been addded by the patch called "flags.mk"
under selftest/powerpc/ folder and is linked to all the Makefile of
powerpc/pmu sub-folders.
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
[mpe: Fixup ifeq, make GIT_VERSION simply expanded to avoid re-executing git describe]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240229093711.581230-2-maddy@linux.ibm.com

tools/testing/selftests/powerpc/flags.mk

+#This checks for any ENV variables and add those.
+
+ifeq ($(GIT_VERSION),)
+GIT_VERSION := $(shell git describe --always --long --dirty || echo "unknown")
+export GIT_VERSION
+endif
+
+ifeq ($(CFLAGS),)
+CFLAGS := -std=gnu99 -O2 -Wall -Werror -DGIT_VERSION='"$(GIT_VERSION)"' -I$(selfdir)/powerpc/include $(CFLAGS)
+export CFLAGS
+endif
+

tools/testing/selftests/powerpc/pmu/Makefile

@@ -7,6 +7,7 @@ EXTRA_SOURCES := ../harness.c event.c lib.c ../utils.c
 
 top_srcdir = ../../../../..
 include ../../lib.mk
+include ../flags.mk
 
 all: $(TEST_GEN_PROGS) ebb sampling_tests event_code_tests
 

tools/testing/selftests/powerpc/pmu/ebb/Makefile

@@ -18,6 +18,7 @@ TEST_GEN_PROGS := reg_access_test event_attributes_test cycles_test	\
 
 top_srcdir = ../../../../../..
 include ../../../lib.mk
+include ../../flags.mk
 
 # The EBB handler is 64-bit code and everything links against it
 CFLAGS += -m64

tools/testing/selftests/powerpc/pmu/event_code_tests/Makefile

@@ -9,6 +9,7 @@ TEST_GEN_PROGS := group_constraint_pmc56_test group_pmc56_exclude_constraints_te
 
 top_srcdir = ../../../../../..
 include ../../../lib.mk
+include ../../flags.mk
 
 CFLAGS += -m64
 

tools/testing/selftests/powerpc/pmu/sampling_tests/Makefile

@@ -9,6 +9,7 @@ TEST_GEN_PROGS := mmcr0_exceptionbits_test mmcr0_cc56run_test mmcr0_pmccext_test
 
 top_srcdir = ../../../../../..
 include ../../../lib.mk
+include ../../flags.mk
 
 CFLAGS += -m64