configure: deal with non-standard libffi installations.

This addresses a failure to build with libffi on
Arch Linux, reported by Joe Eib.

* Makefile (opt/ffi.o, dbg/ffi.o): Pull LIBFFI_CFLAGS
into TXR_CFLAGS for just these object files.

* configure (have_pkgconfig, libffi_cflags): New variables.
(gen_config_make): Create new Makefile variable,
LIBFFI_CFLAGS, from libffi_cflags.
New configure test to detect pkg-config.
Libffi test falls back on using pkg-config to test for
existence of the library and to get the cflags and ldflags.
Any needed cflags end up in LIBFFI_CFLAGS and are used
only when compiling ffi.c.

2 files changed, 29 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index ae3c7fd3..50ee7cdb 100644
--- a/Makefile
+++ b/Makefile
@@ -257,6 +257,10 @@ y.tab.c: $(top_srcdir)parser.y
 # Bison-generated parser also tests for this lint define.
 $(call EACH_CONF,y.tab.o): TXR_CFLAGS += -Dlint
 
+opt/ffi.o: TXR_CFLAGS += $(LIBFFI_CFLAGS)
+
+dbg/ffi.o: TXR_CFLAGS += $(LIBFFI_CFLAGS)
+
 # txr.c needs to know the relative datadir path to do some sysroot
 # calculations.
 
diff --git a/configure b/configure
index c372c80e..235cd819 100755
--- a/configure
+++ b/configure
@@ -143,6 +143,8 @@ have_alloca=
 have_termios=
 have_winsize=
 termios_define=
+have_pkgconfig=
+libffi_cflags=
 
 #
 # Parse configuration variables
@@ -710,6 +712,8 @@ CONF_LDFLAGS := $conf_ldflags
 REMOVE_FLAGS := $remove_flags
 LEX_DBG_FLAGS := $lex_dbg_flags
 TXR_DBG_OPTS := $txr_dbg_opts
+
+LIBFFI_CFLAGS := $libffi_cflags
 !
 }
 
@@ -2828,6 +2832,15 @@ else
   printf "no\n"
 fi
 
+printf "Checking for pkg-config ... "
+
+if pkg-config --version > /dev/null 2>&1 ; then
+  printf "present\n"
+  have_pkgconfig=y
+else
+  printf "absent\n"
+fi
+
 printf "Checking for libffi ... "
 
 cat > conftest.c <<!
@@ -2853,6 +2866,18 @@ elif conftest EXTRA_LDFLAGS=-lffi ; then
   printf "yes\n"
   printf "#define HAVE_LIBFFI 1\n" >> config.h
   conf_ldflags="${conf_ldflags:+"$conf_ldflags "}-lffi"
+elif [ -n "$have_pkgconfig" ] && pkg-config --exists libffi ; then
+  libffi_cflags=$(pkg-config --cflags libffi)
+  libffi_ldflags=$(pkg-config --libs libffi)
+  if conftest EXTRA_CFLAGS="$libffi_cflags" EXTRA_LDFLAGS="$libffi_ldflags" ; then
+    set -x
+    printf "yes\n"
+    printf "#define HAVE_LIBFFI 1\n" >> config.h
+    conf_ldflags="${conf_ldflags:+"$conf_ldflags "}$libffi_ldflags"
+  else
+    printf "no\n"
+    libffi_cflags=
+  fi
 else
   printf "no\n"
 fi