feat: add CFLAGS support

lfs/glibc-2.41.PKGBUILD

@@ -26,9 +26,7 @@ src_prepare() {
 }
 
 src_build() {
-  old_cflags="$CFLAGS"
-  unset CFLAGS
-
+  leaf_clear_flags
   mkdir -pv build
   cd build
   echo "rootsbindir=/usr/sbin" > configparms
@@ -39,8 +37,6 @@ src_build() {
                --disable-nscd                           \
                libc_cv_slibdir=/usr/lib
   make
-
-  export CFLAGS="$old_cflags"
 }
 
 _skip_test() {
@@ -52,15 +48,10 @@ _skip_test() {
 src_check() {
   _skip_test tst-lchmod io/Makefile
 
-  old_cflags="$CFLAGS"
-  unset CFLAGS
   make check
-  export CFLAGS="$old_cflags"
 }
 
 src_install() {
-  old_cflags="$CFLAGS"
-  unset CFLAGS
   cd "${srcdir}/build"
   install -d "${pkgdir}/etc"
   touch "${pkgdir}/etc/ld.so.conf"
@@ -121,8 +112,6 @@ src_install() {
   unset ZONEINFO
 
   install -m644 "${distdir}/${sources[3]}" "${pkgdir}/etc/ld.so.conf"
-
-  export CFLAGS="$old_cflags"
 }
 
 src_preinstall() {