cgo: add support for #cgo noescape lines

Here is the proposal:
https://github.com/golang/go/issues/56378

They are documented here:
https://pkg.go.dev/cmd/cgo@master#hdr-Optimizing_calls_of_C_code

This would have been very useful to fix
https://github.com/tinygo-org/bluetooth/issues/176 in a nice way. That
bug is now fixed in a different way using a wrapper function, but once
this new noescape pragma gets included in TinyGo we could remove the
workaround and use `#cgo noescape` instead.

cgo/testdata/errors.go

@@ -10,6 +10,11 @@ typedef struct {
 
 typedef someType noType; // undefined type
 
+// Some invalid noescape lines
+#cgo noescape
+#cgo noescape foo bar
+#cgo noescape unusedFunction
+
 #define SOME_CONST_1 5) // invalid const syntax
 #define SOME_CONST_2 6) // const not used (so no error)
 #define SOME_CONST_3 1234 // const too large for byte

cgo/testdata/errors.out.go

@@ -1,14 +1,17 @@
 // CGo errors:
+//     testdata/errors.go:14:1: missing function name in #cgo noescape line
+//     testdata/errors.go:15:1: multiple function names in #cgo noescape line
 //     testdata/errors.go:4:2: warning: some warning
 //     testdata/errors.go:11:9: error: unknown type name 'someType'
-//     testdata/errors.go:26:5: warning: another warning
-//     testdata/errors.go:13:23: unexpected token ), expected end of expression
-//     testdata/errors.go:21:26: unexpected token ), expected end of expression
-//     testdata/errors.go:16:33: unexpected token ), expected end of expression
-//     testdata/errors.go:17:34: unexpected token ), expected end of expression
+//     testdata/errors.go:31:5: warning: another warning
+//     testdata/errors.go:18:23: unexpected token ), expected end of expression
+//     testdata/errors.go:26:26: unexpected token ), expected end of expression
+//     testdata/errors.go:21:33: unexpected token ), expected end of expression
+//     testdata/errors.go:22:34: unexpected token ), expected end of expression
 //     -: unexpected token INT, expected end of expression
-//     testdata/errors.go:30:35: unexpected number of parameters: expected 2, got 3
-//     testdata/errors.go:31:31: unexpected number of parameters: expected 2, got 1
+//     testdata/errors.go:35:35: unexpected number of parameters: expected 2, got 3
+//     testdata/errors.go:36:31: unexpected number of parameters: expected 2, got 1
+//     testdata/errors.go:3:1: function "unusedFunction" in #cgo noescape line is not used
 
 // Type checking errors after CGo processing:
 //     testdata/errors.go:102: cannot use 2 << 10 (untyped int constant 2048) as C.char value in variable declaration (overflows)

cgo/testdata/symbols.go

@@ -9,6 +9,10 @@ static void staticfunc(int x);
 
 // Global variable signatures.
 extern int someValue;
+
+void notEscapingFunction(int *a);
+
+#cgo noescape notEscapingFunction
 */
 import "C"
 
@@ -18,6 +22,7 @@ func accessFunctions() {
 	C.variadic0()
 	C.variadic2(3, 5)
 	C.staticfunc(3)
+	C.notEscapingFunction(nil)
 }
 
 func accessGlobals() {

cgo/testdata/symbols.out.go

@@ -75,5 +75,10 @@ func C.staticfunc!symbols.go(x C.int)
 
 var C.staticfunc!symbols.go$funcaddr unsafe.Pointer
 
+//export notEscapingFunction
+//go:noescape
+func C.notEscapingFunction(a *C.int)
+
+var C.notEscapingFunction$funcaddr unsafe.Pointer
 //go:extern someValue
 var C.someValue C.int