autoconf: generate clang's private config.h header

The CMake build already generated one. Follows clang r149497.

This brings us one step closer to compiling and configuring clang
separately from LLVM using the autoconf build, too.

(I lack the right version of autoconf et al. to regen, but it
was a simple change, so I just updated configure manually.)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149498 91177308-0d34-0410-b5e6-96231b3b80d8

autoconf/configure.ac

@@ -1586,7 +1586,10 @@ AC_CONFIG_FILES([llvm.spec])
 
 dnl Configure doxygen's configuration file
 AC_CONFIG_FILES([docs/doxygen.cfg])
+
+dnl Configure clang, if present
 if test -f ${srcdir}/tools/clang/README.txt; then
+  AC_CONFIG_HEADERS([tools/clang/include/clang/Config/config.h])
   AC_CONFIG_FILES([tools/clang/docs/doxygen.cfg])
 fi
 

configure

@@ -21095,6 +21095,7 @@ ac_config_files="$ac_config_files llvm.spec"
 ac_config_files="$ac_config_files docs/doxygen.cfg"
 
 if test -f ${srcdir}/tools/clang/README.txt; then
+  ac_config_headers="$ac_config_headers tools/clang/include/clang/Config/config.h"
   ac_config_files="$ac_config_files tools/clang/docs/doxygen.cfg"
 
 fi