New platform selection system in build system

cmake/platform.cmake

@@ -0,0 +1,44 @@
+macro(subdirlist result curdir)
+    file(GLOB children RELATIVE ${curdir} ${curdir}/*)
+    set(dirlist "")
+    foreach (child ${children})
+        if (IS_DIRECTORY ${curdir}/${child})
+            list(APPEND dirlist ${child})
+        endif()
+    endforeach()
+    set(${result} ${dirlist})
+endmacro()
+
+function (platform_config)
+    set(available_platforms "")
+    set(available_platforms_list "")
+    subdirlist(platforms ${CMAKE_CURRENT_SOURCE_DIR}/photon/libc/sys)
+
+    foreach (platform ${platforms})
+        subdirlist(machines ${CMAKE_CURRENT_SOURCE_DIR}/photon/libc/sys/${platform}/machine)
+        foreach (machine ${machines})
+            set(available_platforms "${available_platforms}${machine}-${platform} ")
+            list(APPEND available_platforms_list ${machine}-${platform})
+        endforeach (machine)
+    endforeach (platform)
+
+    if (${ARGC} LESS 1)
+        message(FATAL_ERROR "No target specified!\n"
+            "Available targets: ${available_platforms}")
+    endif ()
+
+    set(target ${ARGV0})
+
+    list(FIND available_platforms_list ${target} target_idx)
+
+    if (${target_idx} EQUAL -1)
+        message(FATAL_ERROR "${target} is not a valid target!\n"
+        "Available targets: ${available_platforms}")
+    endif ()
+
+    string(REPLACE "-" ";" target_parts ${target})
+    list(GET target_parts 1 platform)
+    list(GET target_parts 0 machine)
+    set(machine ${machine} PARENT_SCOPE)
+    set(platform ${platform} PARENT_SCOPE)
+endfunction (platform_config)