Preserve CFLAGS from the environment.
--- configure.orig	2006-02-21 02:03:22.000000000 -0600
+++ configure	2021-07-06 18:36:00.000000000 -0500
@@ -20864,7 +20864,7 @@
 
 
 
-CFLAGS="-Wall -pipe"
+CFLAGS="${CFLAGS} -Wall -pipe"
 DEBUG_cflags="-g -Wunused -Wshadow -Wpointer-arith -Wbad-function-cast -Wcast-qual -Wcast-align -Wwrite-strings -Wsign-compare -Waggregate-return -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wmissing-noreturn -Wformat -Wredundant-decls -Wnested-externs -Winline -pedantic"
 OPTIMIZE="-O3"
 PROFILE="-g -pg"
