daemon: Fix linking gcrypt when --as-needed linker arg is used

This is a followup to 8a7bd211d2.

As it is mentioned in autoconf manual that library names should be
specified in LIBS, not LDFLAGS. See:

https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.72/html_node/Preset-Output-Variables.html#index-LDFLAGS-2

This change also brings back the save_* vars trick that was there
before. I missed in my earlier change that nix/local.mk was referring
LIBGCRYPT_* vars directly.

And, instead of CXXFLAGS, CPPFLAGS is used since the latter is probably
more correct as this is used for include dirs, therefore using
preprocessor flags.

Tested with ./configure LDFLAGS="-Wl,--as-needed" --with-libgcrypt-prefix=... combinations.

* config-daemon.ac: Set ‘LIBGCRYPT_CPPFLAGS’ instead of
‘LIBGCRYPT_CXXFLAGS’.  Set ‘LIBGCRYPT_LIBS’ in addition to
‘LIBGCRYPT_LDFLAGS’.  Save and restore ‘CPPFLAGS’, ‘LDFLAGS’, and ‘LIBS’
around test.
* nix/local.mk (libutil_a_CPPFLAGS): Add $(LIBGCRYPT_CPPFLAGS).
(libstore_a_CXXFLAGS): Remove $(LIBGCRYPT_CFLAGS).
(guix_daemon_LDFLAGS): New variable.

Change-Id: Iadb10e1994c9a78e2927847af2cfe5e096fbb2a8
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

config-daemon.ac

@@ -39,27 +39,32 @@ if test "x$guix_build_daemon" = "xyes"; then
 
   case "$LIBGCRYPT_PREFIX" in
     no)
-      LIBGCRYPT_CXXFLAGS=""
+      LIBGCRYPT_CPPFLAGS=""
       ;;
     *)
-      LIBGCRYPT_CXXFLAGS="-I$LIBGCRYPT_PREFIX/include"
+      LIBGCRYPT_CPPFLAGS="-I$LIBGCRYPT_PREFIX/include"
       ;;
   esac
 
   case "$LIBGCRYPT_LIBDIR" in
     no | "")
-      LIBGCRYPT_LDFLAGS="-lgcrypt"
       ;;
     *)
-      LIBGCRYPT_LDFLAGS="-L$LIBGCRYPT_LIBDIR -lgcrypt"
+      LIBGCRYPT_LDFLAGS="-L$LIBGCRYPT_LIBDIR"
       ;;
   esac
 
-  AC_SUBST([LIBGCRYPT_CXXFLAGS])
+  LIBGCRYPT_LIBS="-lgcrypt"
+  AC_SUBST([LIBGCRYPT_CPPFLAGS])
   AC_SUBST([LIBGCRYPT_LDFLAGS])
+  AC_SUBST([LIBGCRYPT_LIBS])
 
-  CXXFLAGS="$CXXFLAGS $LIBGCRYPT_CXXFLAGS"
+  save_CPPFLAGS="$CPPFLAGS"
+  save_LDFLAGS="$LDFLAGS"
+  save_LIBS="$LIBS"
+  CPPFLAGS="$CPPFLAGS $LIBGCRYPT_CPPFLAGS"
   LDFLAGS="$LDFLAGS $LIBGCRYPT_LDFLAGS"
+  LIBS="$LIBS $LIBGCRYPT_LIBS"
 
   have_gcrypt=yes
   AC_CHECK_LIB([gcrypt], [gcry_md_open], [:], [have_gcrypt=no])
@@ -67,6 +72,9 @@ if test "x$guix_build_daemon" = "xyes"; then
   if test "x$have_gcrypt" != "xyes"; then
     AC_MSG_ERROR([GNU libgcrypt not found; please install it.])
   fi
+  CPPFLAGS="$save_CPPFLAGS"
+  LDFLAGS="$save_LDFLAGS"
+  LIBS="$save_LIBS"
 
   dnl Chroot support.
   AC_CHECK_FUNCS([chroot unshare])

nix/local.mk

@@ -69,7 +69,8 @@ libutil_headers =				\
 libutil_a_CPPFLAGS =				\
   -I$(top_builddir)/nix				\
   -I$(top_srcdir)/%D%/libutil			\
-  $(libformat_a_CPPFLAGS)
+  $(libformat_a_CPPFLAGS)			\
+  $(LIBGCRYPT_CPPFLAGS)
 
 libstore_a_SOURCES =				\
   %D%/libstore/gc.cc				\
@@ -109,7 +110,7 @@ libstore_a_CPPFLAGS =				\
   -DDEFAULT_CHROOT_DIRS="\"\""
 
 libstore_a_CXXFLAGS = $(AM_CXXFLAGS)		\
-  $(SQLITE3_CFLAGS) $(LIBGCRYPT_CFLAGS)
+  $(SQLITE3_CFLAGS)
 
 bin_PROGRAMS = guix-daemon
 
@@ -122,6 +123,9 @@ guix_daemon_CPPFLAGS =				\
   $(libutil_a_CPPFLAGS)				\
   -I$(top_srcdir)/%D%/libstore
 
+guix_daemon_LDFLAGS = 				\
+  $(LIBGCRYPT_LDFLAGS)
+
 guix_daemon_LDADD =				\
   libstore.a libutil.a libformat.a -lz		\
   $(SQLITE3_LIBS) $(LIBGCRYPT_LIBS)