perf tools: Support Python 3.8+ in Makefile

Python 3.8 changed the output of 'python-config --ldflags' to no longer
include the '-lpythonX.Y' flag (this apparently fixed an issue loading
modules with a statically linked Python executable).  The libpython
feature check in linux/build/feature fails if the Python library is not
included in FEATURE_CHECK_LDFLAGS-libpython variable.

This adds a check in the Makefile to determine if PYTHON_CONFIG accepts
the '--embed' flag and passes that flag alongside '--ldflags' if so.

tools/perf is the only place the libpython feature check is used.
Signed-off-by: Sam Lunt <samuel.j.lunt@gmail.com>
Tested-by: He Zhe <zhe.he@windriver.com>
Link: http://lore.kernel.org/lkml/c56be2e1-8111-9dfe-8298-f7d0f9ab7431@windriver.comAcked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: trivial@kernel.org
Cc: stable@kernel.org
Link: http://lore.kernel.org/lkml/20200131181123.tmamivhq4b7uqasr@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.config

@@ -228,8 +228,17 @@ strip-libs  = $(filter-out -l%,$(1))
 
 PYTHON_CONFIG_SQ := $(call shell-sq,$(PYTHON_CONFIG))
 
+# Python 3.8 changed the output of `python-config --ldflags` to not include the
+# '-lpythonX.Y' flag unless '--embed' is also passed. The feature check for
+# libpython fails if that flag is not included in LDFLAGS
+ifeq ($(shell $(PYTHON_CONFIG_SQ) --ldflags --embed 2>&1 1>/dev/null; echo $$?), 0)
+  PYTHON_CONFIG_LDFLAGS := --ldflags --embed
+else
+  PYTHON_CONFIG_LDFLAGS := --ldflags
+endif
+
 ifdef PYTHON_CONFIG
-  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
+  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) $(PYTHON_CONFIG_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) --includes 2>/dev/null)