build: convert build system to CMake

arch/x86_64/config.cmake

@@ -0,0 +1,5 @@
+target_compile_options(${kernel_exe_name} PRIVATE
+	-z max-page-size=0x1000 -m64 -mcmodel=large -mno-red-zone -mno-mmx
+	-mno-sse -mno-sse2 -D_64BIT -DBYTE_ORDER=1234)
+target_link_libraries(${kernel_exe_name} "-z max-page-size=0x1000" "-T ${CMAKE_CURRENT_SOURCE_DIR}/arch/x86_64/layout.ld")
+

arch/x86_64/targets.cmake

@@ -0,0 +1,7 @@
+find_program(QEMU qemu-system-x86_64)
+
+add_custom_target(run
+	USES_TERMINAL
+	COMMAND ${QEMU}
+		-kernel $<TARGET_FILE:${kernel_exe_name}>
+		-serial stdio)

arch/x86_64/toolchain.cmake

@@ -0,0 +1,18 @@
+# the name of the target operating system
+set(CMAKE_SYSTEM_NAME Magenta)
+
+# which compilers to use for C and C++
+set(CMAKE_C_COMPILER   x86_64-elf-gcc)
+set(CMAKE_ASM_COMPILER   x86_64-elf-gcc)
+set(CMAKE_CXX_COMPILER x86_64-elf-g++)
+
+set(CMAKE_C_COMPILER_WORKS TRUE)
+set(CMAKE_CXX_COMPILER_WORKS TRUE)
+
+# adjust the default behavior of the FIND_XXX() commands:
+# search programs in the host environment
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+
+# search headers and libraries in the target environment
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)