Make the build reproducible with g++-8 and clang-10

Make the build reproducible by removing references to the source
directory from the Catch2WithMain static library.

CMakeLists.txt

@@ -108,6 +108,11 @@ add_library(Catch2WithMain ${CMAKE_CURRENT_LIST_DIR}/src/catch_with_main.cpp)
 target_link_libraries(Catch2WithMain PUBLIC Catch2)
 add_library(Catch2::Catch2WithMain ALIAS Catch2WithMain)
 
+# Make the build reproducible on versions of g++ and clang that supports -ffile-prefix-map
+if(("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" AND NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 8) OR
+   ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" AND NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 10))
+  target_compile_options(Catch2WithMain PRIVATE "-ffile-prefix-map=${CMAKE_SOURCE_DIR}=.")
+endif()
 
 # Only perform the installation steps when Catch is not being used as
 # a subproject via `add_subdirectory`, or the destinations will break,