Fixed library capability detection behaviour.

# Whew! I've fixed all the known problems.
# And should I become a maintainer of this module?

ext/iconv/config.m4

@@ -14,7 +14,8 @@ if test "$PHP_ICONV" != "no"; then
   ])
 
   if test "$iconv_avail" != "no"; then
-
+    iconv_cflags_save="$CFLAGS"
+    CFLAGS="$CFLAGS $INCLUDES"
     AC_MSG_CHECKING([if iconv supports errno])
     AC_TRY_RUN([
 #define LIBICONV_PLUG
@@ -107,6 +108,8 @@ int main() {
         ;;
     esac
 
+    CFLAGS="$iconv_cflags_save"
+
     PHP_NEW_EXTENSION(iconv, iconv.c, $ext_shared)
     PHP_SUBST(ICONV_SHARED_LIBADD)
   else