Allow overriding build settings from the environment

Let packagers pass their own CC, CFLAGS and LDFLAGS settings. The
settings which are specific to dmidecode are appended later so that
they are applied no matter what.

This should fix bug #55805:
https://savannah.nongnu.org/bugs/?55805

Signed-off-by: Jean Delvare <[email protected]>

Author: jdelvare

Makefile

@@ -12,8 +12,13 @@
 #   (at your option) any later version.
 #
 
-CC      = gcc
-CFLAGS  = -W -Wall -Wshadow -Wstrict-prototypes -Wpointer-arith -Wcast-qual \
+CC     ?= gcc
+# Base CFLAGS can be overridden by environment
+CFLAGS ?= -O2
+# When debugging, disable -O2 and enable -g
+#CFLAGS ?= -g
+
+CFLAGS += -W -Wall -Wshadow -Wstrict-prototypes -Wpointer-arith -Wcast-qual \
           -Wcast-align -Wwrite-strings -Wmissing-prototypes -Winline -Wundef
 
 # Let lseek and mmap support 64-bit wide offsets
@@ -22,12 +27,8 @@ CFLAGS += -D_FILE_OFFSET_BITS=64
 #CFLAGS += -DBIGENDIAN
 #CFLAGS += -DALIGNMENT_WORKAROUND
 
-# When debugging, disable -O2 and enable -g.
-CFLAGS += -O2
-#CFLAGS += -g
-
-# Pass linker flags here
-LDFLAGS =
+# Pass linker flags here (can be set from environment too)
+LDFLAGS ?=
 
 DESTDIR =
 prefix  = /usr/local