externals: Add fmt as a submodule

.gitmodules

@@ -1,3 +1,6 @@
+[submodule "externals/fmt"]
+	path = externals/fmt
+	url = https://github.com/fmtlib/fmt.git
 [submodule "externals/xbyak"]
 	path = externals/xbyak
 	url = https://github.com/herumi/xbyak

CMakeLists.txt

@@ -87,6 +87,9 @@ if (DYNARMIC_USE_LLVM)
     llvm_map_components_to_libnames(llvm_libs x86desc x86disassembler)
 endif()
 
+# Pull in externals CMakeLists for libs where available
+add_subdirectory(externals)
+
 # Dynarmic project files
 add_subdirectory(src)
 add_subdirectory(tests)

externals/CMakeLists.txt

@@ -0,0 +1,6 @@
+# For libraries that already come with a CMakeLists file,
+# simply add the directory to that file as a subdirectory
+# to have CMake automatically recognize them.
+
+# fmtlib formatting library
+add_subdirectory(fmt)

src/CMakeLists.txt

@@ -81,3 +81,8 @@ set_target_properties(dynarmic PROPERTIES LINKER_LANGUAGE CXX)
 target_include_directories(dynarmic
                            PUBLIC ../include
                            PRIVATE .)
+# Link fmt
+target_link_libraries(dynarmic PRIVATE fmt-header-only)
+if (CMAKE_SYSTEM_NAME STREQUAL "Windows")
+    target_compile_definitions(dynarmic PRIVATE FMT_USE_WINDOWS_H=0)
+endif()