Realise that the libc core can safely call other libc core functions, even if

they're not defined in the core: so putw() can call stdio stuff, for example.
So the earlier concept of pureness isn't necessary. Rename accordingly.

lang/cem/libcc.ansi/build.lua

@@ -2,12 +2,12 @@ include("plat/build.lua")
 
 tabgen {
 	name = "ctype_tab",
-	srcs = { "./pure/ctype/char.tab" }
+	srcs = { "./core/ctype/char.tab" }
 }
 
 normalrule {
 	name = "ctype_files",
-	ins = { "./pure/ctype/genfiles" },
+	ins = { "./core/ctype/genfiles" },
 	outleaves = {
 		"isalnum.c",
 		"isalpha.c",
@@ -33,14 +33,14 @@ for _, plat in ipairs(vars.plats) do
 		srcs = {
 			"+ctype_files",
 			"+ctype_tab",
-			"./pure/string/*.c",
-			"./pure/stdlib/*.c",
-			"./pure/locale/*.c",
-			"./pure/setjmp/*.c",
-			"./pure/setjmp/*.e",
-			"./pure/math/*.c", -- hypot.c
-			"./pure/math/*.e",
-			"./pure/ctype/*.c",
+			"./core/string/*.c",
+			"./core/stdlib/*.c",
+			"./core/locale/*.c",
+			"./core/setjmp/*.c",
+			"./core/setjmp/*.e",
+			"./core/math/*.c", -- hypot.c
+			"./core/math/*.e",
+			"./core/ctype/*.c",
 			"./errno/*.c",
 			"./malloc/*.c",
 			"./misc/environ.c", -- don't build everything here as it's all obsolete
@@ -56,7 +56,7 @@ for _, plat in ipairs(vars.plats) do
 			"lang/cem/libcc.ansi/headers+pkg",
 			"plat/"..plat.."/include+pkg",
 			"./malloc/malloc.h",
-			"./pure/math/localmath.h",
+			"./core/math/localmath.h",
 			"./stdio/loc_incl.h",
 			"./stdlib/ext_fmt.h",
 			"./time/loc_time.h",

lang/cem/libcc.ansi/core/README.md

@@ -0,0 +1,19 @@
+This directory contains the libc core: functions here may depend on other
+libc functions _only_ (so, no `unistd.h` stuff). Plats don't get to configure
+this, so nothing here should add any overhead if the function isn't linked.
+
+Examples of what goes here:
+
+  - `strcmp()` --- because it's pure code.
+  - `setjmp()` --- in EM, it's portable.
+  - `assert()` --- because it only calls other core functions (`fputs()`
+    and `abort()`).
+
+Examples of what doesn't go here:
+
+  - `malloc()` --- because it calls the `unistd.h` function `sbrk()` (and so a
+    plat might want to swap it out).
+  - stdio --- because it calls the `unistd.h` functions `read()`, `write()`
+    etc.
+  - `signal()` --- because it can't be implemented portably and needs to go
+    in the plat.

lang/cem/libcc.ansi/pure/README.md

@@ -1,3 +0,0 @@
-This directory contains _only_ pure-code libc functions with no dependencies
-on anything other than other pure functions (for example: strcmp, div). There
-should be no reason why any platform won't want these in its libc.