libphobos: Fix link build errors when compiling with unsupported options

The first compilation test to get baseline warnings was getting more
messages due to a missing object.d file, compared to later configure
tests where libphobos is in the include paths.

Because there must always be an object module during compilation, let
the tests themselves be an empty object module instead.

libphobos/ChangeLog:

2019-04-24  Iain Buclaw  <ibuclaw@gdcproject.org>

	PR d/88431
	* configure: Regenerate.
	* m4/libtool.m4 (lt_simple_compile_test_code): Update to not have
	dependencies on libphobos.
	(lt_simple_link_test_code): Likewise.
	(GDCFLAGS): Don't override for D compiler tests.

From-SVN: r270531
diff --git a/libphobos/configure b/libphobos/configure
index 8079a73..7c01989 100755
--- a/libphobos/configure
+++ b/libphobos/configure
@@ -11981,10 +11981,16 @@
 objext_D=$objext
 
 # Code to be used in simple compile tests
-lt_simple_compile_test_code="module mod; extern(C) int main() { return 0; }"
+lt_simple_compile_test_code="\
+  module object;
+  shared int some_variable = 0;
+"
 
 # Code to be used in simple link tests
-lt_simple_link_test_code='module mod; extern(C) int main() { return 0; }'
+lt_simple_link_test_code="\
+  module object;
+  extern(C) int main() { return 0; }
+"
 
 # ltmain only uses $CC for tagged configurations so make sure $CC is set.
 
@@ -12020,12 +12026,9 @@
 # Allow CC to be a program name with arguments.
 lt_save_CC=$CC
 lt_save_CFLAGS=$CFLAGS
-lt_save_DFLAGS=$GDCFLAGS
 lt_save_GCC=$GCC
 GCC=yes
 CC=${GDC-"gdc"}
-# Need to specify location for object.d
-GDCFLAGS="-nophoboslib $GDCFLAGS"
 CFLAGS=$GDCFLAGS
 compiler=$CC
 compiler_D=$CC
@@ -13867,7 +13870,6 @@
 GCC=$lt_save_GCC
 CC=$lt_save_CC
 CFLAGS=$lt_save_CFLAGS
-GDCFLAGS=$lt_save_DFLAGS
 
   GDCFLAGS=$gdc_save_DFLAGS