[multilib] Add support to the autoconf build to substitute

a CLANG_LIBDIR_SUFFIX variable. This is necessary before I can add
support for using that variable to CMake and the C++ code in Clang, and
the autoconf build system does all substitutions in the LLVM tree.

As mentioned before, I'm not planning to add actual multilib support to
the autoconf build, just enough stubs for it to keep playing nicely with
the CMake build once that one has support.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224922 91177308-0d34-0410-b5e6-96231b3b80d8

autoconf/configure.ac

@@ -2017,6 +2017,11 @@ if test "${clang_src_root}" = ""; then
   clang_src_root="$srcdir/tools/clang"
 fi
 if test -f ${clang_src_root}/README.txt; then
+  dnl Clang supports build systems which use the multilib libdir suffix.
+  dnl The autoconf system doesn't support this so stub out that variable.
+  AC_DEFINE_UNQUOTED(CLANG_LIBDIR_SUFFIX,"",
+                     [Multilib suffix for libdir.])
+
   dnl Use variables to stay under 80 columns.
   configh="include/clang/Config/config.h"
   doxy="docs/doxygen.cfg"

configure

@@ -18458,6 +18458,12 @@ if test "${clang_src_root}" = ""; then
   clang_src_root="$srcdir/tools/clang"
 fi
 if test -f ${clang_src_root}/README.txt; then
+
+cat >>confdefs.h <<_ACEOF
+#define CLANG_LIBDIR_SUFFIX ""
+_ACEOF
+
+
     configh="include/clang/Config/config.h"
   doxy="docs/doxygen.cfg"
   ac_config_headers="$ac_config_headers tools/clang/${configh}:${clang_src_root}/${configh}.in"

include/llvm/Config/config.h.in

@@ -9,6 +9,9 @@
 /* Define if we have libxml2 */
 #undef CLANG_HAVE_LIBXML
 
+/* Multilib suffix for libdir. */
+#undef CLANG_LIBDIR_SUFFIX
+
 /* Relative directory for resource files */
 #undef CLANG_RESOURCE_DIR