[AST][RecoveryExpr] Add recovery-ast tests for C language, NFC.

[hokein]

Summary

some examples are working already.

[sammccall]

clang/test/AST/ast-dump-recovery.c

21

why is this an interesting distinct case vs the one above?

40

and this one

56

may or may not want to separate the crash tests out. Up to you, can do this later

[hokein]

address review comments

clang/test/AST/ast-dump-recovery.c

+// RUN: not %clang_cc1 -triple x86_64-unknown-unknown -frecovery-ast -fno-recovery-ast-type -ast-dump %s | FileCheck -strict-whitespace %s
+
+int some_func(int);
+
+// CHECK:     VarDecl {{.*}} unmatch_arg_call 'int' cinit
+// CHECK-NEXT: `-RecoveryExpr {{.*}} contains-errors
+// CHECK-NEXT:   `-DeclRefExpr {{.*}} 'some_func'
+int unmatch_arg_call = some_func();
+
+const int a = 1;
+
+// CHECK:     VarDecl {{.*}} postfix_inc
+// CHECK-NEXT: `-RecoveryExpr {{.*}} contains-errors
+// CHECK-NEXT:   `-DeclRefExpr {{.*}} 'a'
+int postfix_inc = a++;
+
+// CHECK:     VarDecl {{.*}} unary_address
+// CHECK-NEXT:`-RecoveryExpr {{.*}} contains-errors
+// CHECK-NEXT:  `-ParenExpr {{.*}}
+// CHECK-NEXT:    `-BinaryOperator {{.*}} '+'
+// CHECK-NEXT:      |-ImplicitCastExpr
+// CHECK-NEXT:      | `-DeclRefExpr {{.*}} 'a'
+// CHECK-NEXT:      `-IntegerLiteral {{.*}} 'int'
+int unary_address = &(a + 1);
+
+// CHECK:       VarDecl {{.*}} ternary 'int' cinit
+// CHECK-NEXT:  `-RecoveryExpr {{.*}}
+// CHECK-NEXT:    |-DeclRefExpr {{.*}} 'a'
+// CHECK-NEXT:    |-TypoExpr {{.*}}
+// CHECK-NEXT:    `-DeclRefExpr {{.*}} 'a'
+// FIXME: The TypoExpr should never be print, and should be downgraded to
+// RecoveryExpr -- typo correction is performed too early in C-only codepath,
+// which makes no correction when clang finishes the full expr (Sema::Sema::ActOnFinishFullExpr).
+// this will be fixed when we support dependent mechanism and delayed typo correction for C.
+int ternary = a ? undef : a;
+
+void test1() {
+  // CHECK:     `-RecoveryExpr {{.*}} contains-errors
+  // CHECK-NEXT:  `-DeclRefExpr {{.*}} 'a' 'const int'
+  static int foo = a++; // verify no crash on local static var decl.
+}