style(clang-tidy): modularize clang-tidy config

Read blogs and played around with [CMAKE_CXX_CLANG_TIDY](https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_CLANG_TIDY.html).
Also read source code to understand the clang-tidy config of chromium, llvm and other projects.

We can provide complete context including headers to the clang-tidy tool for static analyzer by running it while building the code.
This also makes static analysis first-class citizen of the project, reporting errors before making commits.

For example, `misc-internal-linkage` check was reporting mostly false positives prior to this. With this, it also considered the headers,
where methods/functions were declared constant. Refer #1752

And we should also incrementally add the checks.

Signed-off-by: Balakrishna Avulapati <ba@bavulapati.com>

Author: bavulapati

.clang-tidy

@@ -0,0 +1,4 @@
+---
+# See https://clang.llvm.org/extra/clang-tidy/index.html
+# First disable all default checks (with -*)
+Checks: '-*'

CMakeLists.txt

@@ -22,6 +22,16 @@ option(SOURCEMETA_CORE_CONTRIB_GOOGLEBENCHMARK "Build the GoogleBenchmark librar
 
 include(Sourcemeta)
 
+if(PROJECT_IS_TOP_LEVEL)
+  sourcemeta_target_clang_format(SOURCES
+    src/*.h src/*.cc
+    benchmark/*.h benchmark/*.cc
+    test/*.h test/*.cc)
+  sourcemeta_find_clang_tidy() # Locates CLANG_TIDY program
+endif()
+
+# Add clang-tidy to the targets. Clang-tidy uses the .clang-tidy file for configuration.
+set(CMAKE_CXX_CLANG_TIDY "${CLANG_TIDY_BIN}" "--allow-no-checks")
 # Don't force downstream consumers on it
 if(PROJECT_IS_TOP_LEVEL)
   sourcemeta_enable_simd()
@@ -91,13 +101,6 @@ if(SOURCEMETA_CORE_DOCS)
     OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/website")
 endif()
 
-if(PROJECT_IS_TOP_LEVEL)
-  sourcemeta_target_clang_format(SOURCES
-    src/*.h src/*.cc
-    benchmark/*.h benchmark/*.cc
-    test/*.h test/*.cc)
-  sourcemeta_target_clang_tidy(SOURCES src/*.cc)
-endif()
 
 # Testing
 

cmake/common/targets/clang-tidy.cmake

@@ -0,0 +1,6 @@
+---
+# See https://clang.llvm.org/extra/clang-tidy/index.html
+Checks: 'concurrency-*'
+InheritParentConfig: true
+WarningsAsErrors: '*'
+FormatStyle: none