Revert "[CMake] Use write_basic_package_version_file for LLVM"

This reverts commit 3001d08 which
seems to have introduced a race condition that's failing the build
in some cases.

Author: petrhosek

llvm/cmake/modules/CMakeLists.txt

@@ -127,13 +127,11 @@ configure_file(
   ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/LLVMConfig.cmake
   @ONLY)
 
-# Generate LLVMConfigVersion.cmake for build tree (later copied to install tree).
-include(CMakePackageConfigHelpers)
-write_basic_package_version_file(
-  "${llvm_cmake_builddir}/LLVMConfigVersion.cmake"
-  VERSION "${PACKAGE_VERSION}"
-  COMPATIBILITY SameMinorVersion
-)
+# Generate LLVMConfigVersion.cmake for build and install tree.
+configure_file(
+  LLVMConfigVersion.cmake.in
+  ${llvm_cmake_builddir}/LLVMConfigVersion.cmake
+  @ONLY)
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   get_property(llvm_has_exports GLOBAL PROPERTY LLVM_HAS_EXPORTS)

llvm/cmake/modules/LLVMConfigVersion.cmake.in

@@ -0,0 +1,13 @@
+set(PACKAGE_VERSION "@PACKAGE_VERSION@")
+
+# LLVM is API-compatible only with matching major.minor versions
+# and patch versions not less than that requested.
+if("@LLVM_VERSION_MAJOR@.@LLVM_VERSION_MINOR@" VERSION_EQUAL
+    "${PACKAGE_FIND_VERSION_MAJOR}.${PACKAGE_FIND_VERSION_MINOR}"
+   AND NOT "@LLVM_VERSION_PATCH@" VERSION_LESS "${PACKAGE_FIND_VERSION_PATCH}")
+  set(PACKAGE_VERSION_COMPATIBLE 1)
+  if("@LLVM_VERSION_PATCH@" VERSION_EQUAL
+      "${PACKAGE_FIND_VERSION_PATCH}")
+    set(PACKAGE_VERSION_EXACT 1)
+  endif()
+endif()