Build: enable C++20 and updated all compiler requirements

* ported some header and cmake updates from master branch

cmake/compiler/clang/settings.cmake

@@ -3,6 +3,14 @@ target_compile_definitions(trinity-compile-option-interface
   INTERFACE
     -D_BUILD_DIRECTIVE="$<CONFIG>")
 
+set(CLANG_EXPECTED_VERSION 11.0.0)
+
+if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS CLANG_EXPECTED_VERSION)
+  message(FATAL_ERROR "Clang: TrinityCore requires version ${CLANG_EXPECTED_VERSION} to build but found ${CMAKE_CXX_COMPILER_VERSION}")
+else()
+  message(STATUS "Clang: Minimum version required is ${CLANG_EXPECTED_VERSION}, found ${CMAKE_CXX_COMPILER_VERSION} - ok!")
+endif()
+
 if(WITH_WARNINGS)
   target_compile_options(trinity-warning-interface
     INTERFACE
@@ -52,3 +60,13 @@ if(BUILD_SHARED_LIBS)
 
   message(STATUS "Clang: Disallow undefined symbols")
 endif()
+
+# speedup PCH builds by forcing template instantiations during PCH generation
+set(CMAKE_REQUIRED_FLAGS "-fpch-instantiate-templates")
+check_cxx_source_compiles("int main() { return 0; }" CLANG_HAS_PCH_INSTANTIATE_TEMPLATES)
+unset(CMAKE_REQUIRED_FLAGS)
+if(CLANG_HAS_PCH_INSTANTIATE_TEMPLATES)
+  target_compile_options(trinity-compile-option-interface
+    INTERFACE
+      -fpch-instantiate-templates)
+endif()