[SV 60378] Don't add duplicate default search directories

Depending on how make was configured it may add duplicate
directories in the default include search path: avoid this.

(Tweaked by psmith@gnu.org)

* configure.ac: Set AM variable KNOWN_PREFIX if --prefix is known
* Makefile.am: Only set INCLUDEDIR if prefix is not known
* read.c [default_include_directories]: Only add INCLUDEDIR if set

Makefile.am

@@ -73,8 +73,12 @@ make_LDADD =	$(LIBOBJS) $(_GUILE_LIBS) lib/libgnu.a $(GETLOADAVG_LIBS) \
 localedir =	$(datadir)/locale
 
 AM_CPPFLAGS =	-Isrc -I$(top_srcdir)/src -Ilib -I$(top_srcdir)/lib \
-		-DLIBDIR=\"$(libdir)\" -DINCLUDEDIR=\"$(includedir)\" \
-		-DLOCALEDIR=\"$(localedir)\"
+		-DLIBDIR=\"$(libdir)\" -DLOCALEDIR=\"$(localedir)\"
+
+# If prefix is not a standard location, look in prefix as well
+if !KNOWN_PREFIX
+  AM_CPPFLAGS += -DINCLUDEDIR=\"$(includedir)\"
+endif
 
 AM_CFLAGS =	$(_GUILE_CFLAGS)
 

configure.ac

@@ -523,6 +523,11 @@ AS_IF([test "x$make_cv_posix_spawn" = xno && test "x$user_posix_spawn" = xyes],
   echo
 ])
 
+# autoconf initializes $prefix to NONE.
+AM_CONDITIONAL([KNOWN_PREFIX],
+               [test "x$prefix" = xNONE -o "x$prefix" = x/usr/local \
+                     -o "x$prefix" = x/usr/gnu -o "x$prefix" = x/usr])
+
 # Specify what files are to be created.
 AC_CONFIG_FILES([Makefile build.cfg lib/Makefile po/Makefile.in doc/Makefile \
                  tests/config-flags.pm])

src/read.c

@@ -107,7 +107,9 @@ static const char *default_include_directories[] =
    This is defined as a placeholder.  */
 # define INCLUDEDIR "."
 #endif
+#if defined(INCLUDEDIR)
     INCLUDEDIR,
+#endif
 #ifndef _AMIGA
     "/usr/gnu/include",
     "/usr/local/include",