autoconf: Pass CFLAGS from configure to apxs.

To allow the user to specify CFLAGS in configure, add the CFLAGS macro
to the generated `apxs` command line. This allows us to run things like:

    ./configure CFLAGS=-Werror

Author: olavmo-sikt

Makefile.in

@@ -25,7 +25,7 @@ DISTFILES=$(SRC) \
 all:	mod_auth_mellon.la
 
 mod_auth_mellon.la: $(SRC) auth_mellon.h auth_mellon_compat.h
-	@APXS2@ -Wc,"-std=c99 @OPENSSL_CFLAGS@ @LASSO_CFLAGS@ @CURL_CFLAGS@ @GLIB_CFLAGS@" -Wl,"@OPENSSL_LIBS@ @LASSO_LIBS@ @CURL_LIBS@ @GLIB_LIBS@" -Wc,-Wall -Wc,-g -c $(SRC)
+	@APXS2@ -Wc,"-std=c99 @OPENSSL_CFLAGS@ @LASSO_CFLAGS@ @CURL_CFLAGS@ @GLIB_CFLAGS@ @CFLAGS@" -Wl,"@OPENSSL_LIBS@ @LASSO_LIBS@ @CURL_LIBS@ @GLIB_LIBS@" -Wc,-Wall -Wc,-g -c $(SRC)
 
 
 # Building configure (for distribution)