perf tools: Pass PYTHON config to feature detection

( This is a rebased version of https://lkml.org/lkml/2017/2/7/662 )

Python's CC and link Makefile variables were not passed to feature
detection, causing feature detection to use system's Python rather than
PYTHON_CONFIG's one. This created a mismatch between the detected Python
support and the one actually used by perf when PYTHON_CONFIG is
specified.

Fix it by moving Python's variable initialization to before feature
detection and pass FLAGS_PYTHON_EMBED to Python's feature detection's
build target.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Simon Que <sque@chromium.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170412064919.92449-2-davidcc@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/feature/Makefile

@@ -175,7 +175,7 @@ $(OUTPUT)test-libperl.bin:
 	$(BUILD) $(FLAGS_PERL_EMBED)
 
 $(OUTPUT)test-libpython.bin:
-	$(BUILD)
+	$(BUILD) $(FLAGS_PYTHON_EMBED)
 
 $(OUTPUT)test-libpython-version.bin:
 	$(BUILD)

tools/perf/Makefile.config

@@ -170,13 +170,20 @@ PYTHON2_CONFIG := \
 override PYTHON_CONFIG := \
   $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON2_CONFIG))
 
+grep-libs  = $(filter -l%,$(1))
+strip-libs  = $(filter-out -l%,$(1))
+
 PYTHON_CONFIG_SQ := $(call shell-sq,$(PYTHON_CONFIG))
 
-PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
-PYTHON_EMBED_CCOPTS := $(shell $(PYTHON_CONFIG_SQ) --cflags 2>/dev/null)
-
-ifeq ($(CC), clang)
-  PYTHON_EMBED_CCOPTS := $(filter-out -specs=%,$(PYTHON_EMBED_CCOPTS))
+ifdef PYTHON_CONFIG
+  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
+  PYTHON_EMBED_LDFLAGS := $(call strip-libs,$(PYTHON_EMBED_LDOPTS))
+  PYTHON_EMBED_LIBADD := $(call grep-libs,$(PYTHON_EMBED_LDOPTS)) -lutil
+  PYTHON_EMBED_CCOPTS := $(shell $(PYTHON_CONFIG_SQ) --cflags 2>/dev/null)
+  ifeq ($(CC), clang)
+    PYTHON_EMBED_CCOPTS := $(filter-out -specs=%,$(PYTHON_EMBED_CCOPTS))
+  endif
+  FLAGS_PYTHON_EMBED := $(PYTHON_EMBED_CCOPTS) $(PYTHON_EMBED_LDOPTS)
 endif
 
 FEATURE_CHECK_CFLAGS-libpython := $(PYTHON_EMBED_CCOPTS)
@@ -554,8 +561,6 @@ ifndef NO_GTK2
   endif
 endif
 
-grep-libs  = $(filter -l%,$(1))
-strip-libs = $(filter-out -l%,$(1))
 
 ifdef NO_LIBPERL
   CFLAGS += -DNO_LIBPERL
@@ -603,21 +608,9 @@ else
       $(call disable-python,No 'python-config' tool was found: disables Python support - please install python-devel/python-dev)
     else
 
-      PYTHON_CONFIG_SQ := $(call shell-sq,$(PYTHON_CONFIG))
-
-      PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
-      PYTHON_EMBED_LDFLAGS := $(call strip-libs,$(PYTHON_EMBED_LDOPTS))
-      PYTHON_EMBED_LIBADD := $(call grep-libs,$(PYTHON_EMBED_LDOPTS)) -lutil
-      PYTHON_EMBED_CCOPTS := $(shell $(PYTHON_CONFIG_SQ) --cflags 2>/dev/null)
-      ifeq ($(CC), clang)
-        PYTHON_EMBED_CCOPTS := $(filter-out -specs=%,$(PYTHON_EMBED_CCOPTS))
-      endif
-      FLAGS_PYTHON_EMBED := $(PYTHON_EMBED_CCOPTS) $(PYTHON_EMBED_LDOPTS)
-
       ifneq ($(feature-libpython), 1)
         $(call disable-python,No 'Python.h' (for Python 2.x support) was found: disables Python support - please install python-devel/python-dev)
       else
-
         ifneq ($(feature-libpython-version), 1)
           $(warning Python 3 is not yet supported; please set)
           $(warning PYTHON and/or PYTHON_CONFIG appropriately.)