Merge pull request #14 from JuliaLang/sf/fixes

Makefile fixes

Makefile

@@ -10,15 +10,20 @@ OBJCONV = objconv
 
 CPPFLAGS_add = -I$(LIBOSXUNWIND_HOME)/src -I$(LIBOSXUNWIND_HOME)/include -DNDEBUG
 CFLAGS_add = -std=c99 -Wall -O3
+CXXFLAGS_add = -std=c++11 -Wall -O3
+LDFLAGS_add = -nodefaultlibs -Wl,-upward-lSystem -Wl,-umbrella,System
 SFLAGS_add = -x assembler-with-cpp
 
+# If `-stdlib=` is specified within our environment variables, then don't add another command line argument asking to link against it..
+ifneq (,$(findstring -stdlib=,$(CC) $(CPPFLAGS) $(CXXFLAGS)))
+# If our clang is new enough, then we need to add in `-stdlib=libstdc++`.
 CLANG_MAJOR_VER := $(shell clang -v 2>&1 | grep LLVM | cut -d' ' -f 4 | cut -d'.' -f 1)
 ifeq ($(shell [ $(CLANG_MAJOR_VER) -ge 8 ] && echo true),true)
-CXXFLAGS_add = -std=c++11 -stdlib=libstdc++ -Wall -O3
-LDFLAGS_add = -nodefaultlibs -stdlib=libstdc++ -Wl,-upward-lSystem -Wl,-umbrella,System
+CXXFLAGS_add += -stdlib=libstdc++
+LDFLAGS_add += -stdlib=libstdc++
 else
-CXXFLAGS_add = -std=c++11 -Wall -O3
-LDFLAGS_add = -nodefaultlibs -Wl,-upward-lSystem -Wl,-umbrella,System -lstdc++
+LDFLAGS_add += -lstdc++
+endif
 endif
 
 # Files (in src/)
@@ -60,7 +65,8 @@ OBJS = 	$(patsubst %.c,%.c.o,			\
 	$(CC) $(CPPFLAGS_add) $(CPPFLAGS) $(CXXFLAGS_add) $(CXXFLAGS) -c $< -o $@
 
 %.s.o: %.s
-	$(CC) $(SFLAGS) $(SFLAGS_add) $(filter -m% -B% -I% -D%,$(CFLAGS_add)) -c $< -o $@
+	$(CC) $(SFLAGS_add) $(SFLAGS) $(filter -m% -B% -I% -D%,$(CFLAGS_add)) -c $< -o $@
+
 
 
 libosxunwind.a: $(OBJS)  
@@ -77,4 +83,4 @@ libosxunwind.dylib: $(OBJS)
 clean:
 	rm -f $(OBJS) *.a *.dylib
 distclean: clean
-	
+.SUFFIXES: .cxx