Teach LLVMConfigVersion.cmake to behave as find_package() expects.

Patch by Brad King

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206426 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/LLVMConfigVersion.cmake.in

@@ -1 +1,13 @@
-set(PACKAGE_VERSION "@PACKAGE_VERSION@")
+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()

cmake/modules/Makefile

@@ -52,6 +52,9 @@ $(PROJ_OBJ_DIR)/LLVMConfigVersion.cmake: LLVMConfigVersion.cmake.in
 	$(Echo) 'Generating LLVM CMake package version file'
 	$(Verb) cat $< | sed \
 	  -e 's/@PACKAGE_VERSION@/'"$(LLVMVersion)"'/' \
+	  -e 's/@LLVM_VERSION_MAJOR@/'"$(LLVM_VERSION_MAJOR)"'/' \
+	  -e 's/@LLVM_VERSION_MINOR@/'"$(LLVM_VERSION_MINOR)"'/' \
+	  -e 's/@LLVM_VERSION_PATCH@/'"$(LLVM_VERSION_PATCH)"'/' \
 	  > $@
 
 $(PROJ_OBJ_DIR)/LLVMExports.cmake: $(LLVMBuildCMakeExportsFrag)