bpo-40280: Add wasm cross build targets

CPython uses the same target triplet convention as Rust:

```
$ rustc --print target-list | grep wasm
wasm32-unknown-emscripten
wasm32-unknown-unknown
wasm32-wasi
wasm64-unknown-unknown
```

Signed-off-by: Christian Heimes <[email protected]>

Author: tiran

Misc/NEWS.d/next/Build/2021-11-25-10-55-03.bpo-40280.E9-gsQ.rst

@@ -0,0 +1,3 @@
+``configure`` now accepts machine ``wasm32`` or ``wasm64`` and OS ``wasi``
+or ``emscripten`` for cross building, e.g. ``wasm32-unknown-emscripten``
+and ``wasm32-wasi``.

configure

@@ -3717,6 +3717,12 @@ then
 	*-*-vxworks*)
 	    ac_sys_system=VxWorks
 	    ;;
+	*-*-emscripten)
+	    ac_sys_system=Emscripten
+	    ;;
+	*-*-wasi)
+	    	    ac_sys_system=wasi
+	    ;;
 	*)
 		# for now, limit cross builds to known configurations
 		MACHDEP="unknown"
@@ -3767,6 +3773,9 @@ if test "$cross_compiling" = yes; then
 	*-*-vxworks*)
 		_host_cpu=$host_cpu
 		;;
+	wasm32-*-* | wasm64-*-*)
+		_host_cpu=$host_cpu
+		;;
 	*)
 		# for now, limit cross builds to known configurations
 		MACHDEP="unknown"
@@ -10382,6 +10391,9 @@ fi
 	# Dynamic linking for HP-UX
 
 
+
+
+
 have_uuid=missing
 
 for ac_header in uuid.h
@@ -10414,10 +10426,6 @@ fi
 done
 
 
-
-
-
-
 if test "x$have_uuid" = xmissing; then :
 
 

configure.ac

@@ -465,6 +465,13 @@ then
 	*-*-vxworks*)
 	    ac_sys_system=VxWorks
 	    ;;
+	*-*-emscripten)
+	    ac_sys_system=Emscripten
+	    ;;
+	*-*-wasi)
+	    dnl wasm32-wasi, wasm32-unknown-wasi
+	    ac_sys_system=wasi
+	    ;;
 	*)
 		# for now, limit cross builds to known configurations
 		MACHDEP="unknown"
@@ -514,6 +521,9 @@ if test "$cross_compiling" = yes; then
 	*-*-vxworks*)
 		_host_cpu=$host_cpu
 		;;
+	wasm32-*-* | wasm64-*-*)
+		_host_cpu=$host_cpu
+		;;
 	*)
 		# for now, limit cross builds to known configurations
 		MACHDEP="unknown"