Change union layout to store type info rather than an integer; ternary expression for types with constant condition

core/c.odin

@@ -0,0 +1,41 @@
+CHAR_BIT :: 8;
+
+c_bool           :: bool;
+
+c_char           :: u8;
+
+c_schar          :: i8;
+c_uchar          :: i8;
+
+c_short          :: i16;
+c_ushort         :: i16;
+
+c_int            :: i32;
+c_uint           :: u32;
+
+c_long  :: ODIN_OS == "windows" ?
+	i32 :
+	(size_of(int) == 4) ?
+		i32 :
+		i64;
+
+c_ulong :: ODIN_OS == "windows" ?
+	u32 :
+	(size_of(int) == 4) ?
+		u32 :
+		u64;
+
+c_longlong       :: i64;
+c_ulonglong      :: u64;
+
+c_float          :: f32;
+c_double         :: f64;
+
+c_complex_float  :: complex64;
+c_complex_double :: complex128;
+
+c_size_t         :: uint;
+c_ssize_t        :: int;
+c_ptrdiff_t      :: int;
+c_uintptr_t      :: uint;
+c_intptr_t       :: int;