tools build: Add feature detection for g++

Check if g++ is available. The result will be used by builtin clang and
LLVM support. Since LLVM requires C++11, this feature detector checks
std::move().

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1474874832-134786-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.feature

@@ -7,7 +7,7 @@ endif
 
 feature_check = $(eval $(feature_check_code))
 define feature_check_code
-  feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
+  feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
 endef
 
 feature_set = $(eval $(feature_set_code))

tools/build/feature/Makefile

@@ -46,11 +46,13 @@ FILES=					\
 	test-lzma.bin			\
 	test-bpf.bin			\
 	test-get_cpuid.bin		\
-	test-sdt.bin
+	test-sdt.bin			\
+	test-cxx.bin
 
 FILES := $(addprefix $(OUTPUT),$(FILES))
 
 CC := $(CROSS_COMPILE)gcc -MD
+CXX := $(CROSS_COMPILE)g++ -MD
 PKG_CONFIG := $(CROSS_COMPILE)pkg-config
 
 all: $(FILES)
@@ -58,6 +60,9 @@ all: $(FILES)
 __BUILD = $(CC) $(CFLAGS) -Wall -Werror -o $@ $(patsubst %.bin,%.c,$(@F)) $(LDFLAGS)
   BUILD = $(__BUILD) > $(@:.bin=.make.output) 2>&1
 
+__BUILDXX = $(CXX) $(CXXFLAGS) -Wall -Werror -o $@ $(patsubst %.bin,%.cpp,$(@F)) $(LDFLAGS)
+  BUILDXX = $(__BUILDXX) > $(@:.bin=.make.output) 2>&1
+
 ###############################
 
 $(OUTPUT)test-all.bin:
@@ -217,6 +222,9 @@ $(OUTPUT)test-bpf.bin:
 $(OUTPUT)test-sdt.bin:
 	$(BUILD)
 
+$(OUTPUT)test-cxx.bin:
+	$(BUILDXX) -std=gnu++11
+
 -include $(OUTPUT)*.d
 
 ###############################

tools/build/feature/test-cxx.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <memory>
+
+static void print_str(std::string s)
+{
+	std::cout << s << std::endl;
+}
+
+int main()
+{
+	std::string s("Hello World!");
+	print_str(std::move(s));
+	std::cout << "|" << s << "|" << std::endl;
+	return 0;
+}