extend global CFLAGS and LDFLAGS to aid distro packaging

This preserves globally defined CFLAGS and LDFLAGS and simply
extends those variables to aid distro based packaging toolchains
and predefined distro wide defaults like SSP, relro etc.

src/Makefile

@@ -90,7 +90,7 @@ VERSION_TAG              := $(shell test -d .git && git describe --tags --dirty=
 ## Compiler flags
 ##
 
-CFLAGS                   := -pipe -W -Wall -std=c99 -Iinclude/ -IOpenCL/ -I$(OPENCL_HEADERS_KHRONOS)/
+CFLAGS                   += -pipe -W -Wall -std=c99 -Iinclude/ -IOpenCL/ -I$(OPENCL_HEADERS_KHRONOS)/
 
 ifndef DEBUG
 CFLAGS                   += -O2
@@ -112,6 +112,7 @@ export MACOSX_DEPLOYMENT_TARGET=10.9
 CFLAGS_NATIVE            := -D_POSIX -DDARWIN
 CFLAGS_NATIVE            += $(CFLAGS)
 LFLAGS_NATIVE            := -lpthread
+LFLAGS_NATIVE            += $(LDFLAGS)
 endif # darwin
 
 ifeq ($(UNAME),Linux)
@@ -122,6 +123,7 @@ endif
 CFLAGS_NATIVE            += $(CFLAGS)
 LFLAGS_NATIVE            := -lpthread -ldl
 CFLAGS_NATIVE            += -DHAVE_HWMON
+LFLAGS_NATIVE            += $(LDFLAGS)
 endif # linux
 
 ##