externals: Make catch an interface target

Eliminates top-level inclusion of the headers with include_directories()
and instead utilizes it on a by-target basis using target_include_directories().

CMakeLists.txt

@@ -111,9 +111,8 @@ else()
 endif()
 include_directories(${Boost_INCLUDE_DIRS})
 
-# Include Catch
-include_directories(externals/catch)
-enable_testing(true)  # Enables unit-testing.
+# Enable unit-testing.
+enable_testing(true)
 
 # Include LLVM
 if (DYNARMIC_USE_LLVM)

externals/CMakeLists.txt

@@ -13,3 +13,7 @@ if (NOT TARGET xbyak)
         target_include_directories(xbyak INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/xbyak/xbyak)
     endif()
 endif()
+
+add_library(catch INTERFACE)
+target_include_directories(catch INTERFACE
+                           $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/catch>)

tests/CMakeLists.txt

@@ -35,7 +35,7 @@ include(CreateDirectoryGroups)
 create_directory_groups(${SRCS} ${HEADERS})
 
 add_executable(dynarmic_tests ${SRCS})
-target_link_libraries(dynarmic_tests dynarmic ${llvm_libs})
+target_link_libraries(dynarmic_tests dynarmic catch ${llvm_libs})
 set_target_properties(dynarmic_tests PROPERTIES LINKER_LANGUAGE CXX)
 target_include_directories(dynarmic_tests PRIVATE . ../src)
 target_compile_options(dynarmic_tests PRIVATE ${DYNARMIC_CXX_FLAGS})