Try to support building and running on Travis

This was previously working for my local LLVM build.  Now I want it to
work on Travis, so I have prepared a release of clang-tidy that's
suitable to run there, and set it up to work with either version.

CMakeLists.txt

@@ -8,6 +8,8 @@ SET(CMAKE_MODULE_PATH
     ${CMAKE_SOURCE_DIR}/CMakeModules
 )
 
+SET(CMAKE_TLS_VERIFY ON)
+
 # Build options
 option(TILES        "Build graphical tileset version."						"OFF")
 option(CURSES       "Build curses version."							"ON" )

tools/clang-tidy-plugin/CMakeLists.txt

@@ -1,12 +1,49 @@
+include(ExternalProject)
+
+find_package(LLVM REQUIRED CONFIG)
+find_package(Clang REQUIRED CONFIG)
+
 add_library(
     CataAnalyzerPlugin MODULE
     CataTidyModule.cpp NoLongCheck.cpp)
-MESSAGE("Building clang-tidy plugin with include paths: ${LLVM_INCLUDE_DIRS}")
-if ("${LLVM_INCLUDE_DIRS}" STREQUAL "")
+
+target_include_directories(
+    CataAnalyzerPlugin SYSTEM PRIVATE
+    ${LLVM_INCLUDE_DIRS} ${CLANG_INCLUDE_DIRS})
+
+if ("${CATA_CLANG_TIDY_INCLUDE_DIR}" STREQUAL "")
+    SET(ctps_releases
+        https://github.com/jbytheway/clang-tidy-plugin-support/releases/download)
+    SET(ctps_version llvm-8.0.1-r12)
+    SET(ctps_src
+        ${CMAKE_CURRENT_BINARY_DIR}/clang-tidy-plugin-support)
+
+    ExternalProject_Add(
+        clang-tidy-plugin-support
+        URL ${ctps_releases}/${ctps_version}/clang-tidy-plugin-support-${ctps_version}.tar.xz
+        URL_HASH SHA256=00ffab0df11250f394830735514c62ae787bd2eb6eb9d5e97471206d270c54e2
+        SOURCE_DIR ${ctps_src}
+        CONFIGURE_COMMAND ""
+        BUILD_COMMAND ""
+        INSTALL_COMMAND ""
+        TEST_COMMAND ""
+    )
+
+    add_dependencies(CataAnalyzerPlugin clang-tidy-plugin-support)
+    target_include_directories(
+        CataAnalyzerPlugin SYSTEM PRIVATE ${ctps_src}/include)
 else()
     target_include_directories(
-        CataAnalyzerPlugin SYSTEM PRIVATE ${LLVM_INCLUDE_DIRS})
+        CataAnalyzerPlugin SYSTEM PRIVATE ${CATA_CLANG_TIDY_INCLUDE_DIR})
 endif()
+
+target_compile_definitions(
+    CataAnalyzerPlugin PRIVATE ${LLVM_DEFINITIONS})
+
+# We need to turn off exceptions and RTTI to match the LLVM build.
+# I feel there ought to be a way to extract these flags from the
+# LLVMConfig.cmake as we have done for e.g. LLVM_INCLUDE_DIRS above, but I
+# haven't found one.
 if(MSVC)
 else()
     target_compile_options(