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.

this re-fixes 7f8aaf7430 after it was
somehow undone ;)

src/Makefile

@@ -101,7 +101,7 @@ BINARY_NATIVE           := $(PROG_NAME)
 ## General compiler and linker options
 ##
 
-CFLAGS                  := -pipe -std=c99 -Iinclude/ -IOpenCL/
+CFLAGS                  += -pipe -std=c99 -Iinclude/ -IOpenCL/
 CFLAGS                  += -W
 CFLAGS                  += -Wall
 CFLAGS                  += -Wextra
@@ -137,7 +137,7 @@ CFLAGS                  += -ftrapv
 
 #CFLAGS                  += -Wstack-usage=524288
 
-LFLAGS                  :=
+LFLAGS                  := $(LDFLAGS)
 
 ifndef DEBUG
 CFLAGS                  += -O2