Move ODIN_* platform constants to core:os

core/os/os_amd64.odin

@@ -0,0 +1,4 @@
+package os;
+
+ARCH :: "amd64";
+ENDIAN :: "little";

core/os/os_essence.odin

@@ -1,5 +1,7 @@
 package os
 
+OS :: "essence";
+
 // foreign import api "system:api"
 
 // Handle    :: distinct int;

core/os/os_linux.odin

@@ -6,6 +6,8 @@ foreign import libc "system:c"
 import "core:strings"
 import "core:mem"
 
+OS :: "linux";
+
 Handle    :: distinct i32;
 File_Time :: distinct u64;
 Errno     :: distinct i32;

core/os/os_osx.odin

@@ -6,6 +6,8 @@ foreign import libc "system:c"
 import "core:strings"
 import "core:mem"
 
+OS :: "osx";
+
 Handle    :: distinct i32;
 File_Time :: distinct u64;
 Errno     :: distinct int;

core/os/os_windows.odin

@@ -3,6 +3,8 @@ package os
 import "core:sys/win32"
 import "core:mem"
 
+OS :: "windows";
+
 Handle    :: distinct uintptr;
 File_Time :: distinct u64;
 Errno     :: distinct int;

core/os/os_x86.odin

@@ -0,0 +1,4 @@
+package os;
+
+ARCH :: "x86";
+ENDIAN :: "little";