sys/src: move arches to sys src so it can be shared

Signed-off-by: Sevki <s@sevki.org>

sys/src/9/boot/BUILD

@@ -1,10 +1,5 @@
 load("//sys/src/FLAGS", "LIB_COMPILER_FLAGS")
-
-ARCHS = [
-	"amd64",
-	"riscv",
-	"aarch64",
-]
+load("//sys/src/ARCHS", "ARCHS")
 
 [mk_sys(
 	name="boot%scpuc" % arch,

sys/src/ARCHS

@@ -0,0 +1,5 @@
+ARCHS = [
+	"amd64",
+	"riscv",
+	"aarch64",
+]