build: serialise `LLVM_ENABLE_UNWIND_TABLES` into LLVMConfig

Serialize the value of the configuration option into the configuration so that
builds which integrate LLVM can identify the value of the flag that was used to
build the libraries.  This is intended to be used by Swift to control tests
which rely on the unwind information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373253 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/LLVMConfig.cmake.in

@@ -45,6 +45,8 @@ set(LLVM_ENABLE_TERMINFO @LLVM_ENABLE_TERMINFO@)
 
 set(LLVM_ENABLE_THREADS @LLVM_ENABLE_THREADS@)
 
+set(LLVM_ENABLE_UNWIND_TABLES @LLVM_ENABLE_UNWIND_TABLES@)
+
 set(LLVM_ENABLE_ZLIB @LLVM_ENABLE_ZLIB@)
 
 set(LLVM_LIBXML2_ENABLED @LLVM_LIBXML2_ENABLED@)