build: Do not mess with CFLAGS in configure.

* configure.ac: Do not mess with the user provided CFLAGS.
--

A problem was claimed with some configure tests if the user provided
CFLAGS=-Werror.  The commit introducing this

Fixes-commit: 02eb9fc9d5

does not mention a concrete case.  Anyway, messing with CFLAGS is a
bad idea because configure tests will then test something different
than what is used later (cf. autoconf manual).  Tests which depend on
the whether -Werror is used needsto be fixed.

Note that in certain cases we modify CFLAGS.  This is only done for
some configure options or if the platform requires the use of special
compiler flags (e.g. on HP/UX).

GnuPG-bug-id: 2423

configure.ac

@@ -89,12 +89,6 @@ AB_INIT
 
 AC_GNU_SOURCE
 
-# Before we do anything with the C compiler, we first save the user's
-# CFLAGS (they are restored at the end of the configure script).  This
-# is because some configure checks don't work with -Werror, but we'd
-# like to use -Werror with our build.
-CFLAGS_orig=$CFLAGS
-CFLAGS=
 
 # Some status variables.
 have_gpg_error=no
@@ -1700,11 +1694,6 @@ if test x"$gnupg_builddir_envvar" = x"yes"; then
       [This is only used with "make distcheck"])
 fi
 
-#
-# Add user CFLAGS.
-#
-CFLAGS="$CFLAGS $CFLAGS_orig"
-
 #
 # Decide what to build
 #