Lex: Don't try to recover as hard in malformed _Pragma

[majnemer]

Summary

It's not particularly safe to lex a token if you don't know what it is.
_Pragma error recovery attempted to lex tokens without being sure what
they might be.

[majnemer]

Ping.

[rnk]

See Richard's mail on cfe-commits:

Can you include both an EOD test and an EOF test? Otherwise, LGTM.

lib/Lex/Pragma.cpp

if (Tok.isNot(tok::l_paren)) {
     Diag(PragmaLoc, diag::err__Pragma_malformed);
     return _PragmaLexing.failed();
   }
 
   // Read the '"..."'.
   Lex(Tok);
   if (!tok::isStringLiteral(Tok.getKind())) {
     Diag(PragmaLoc, diag::err__Pragma_malformed);
-    // Skip this token, and the ')', if present.
-    if (Tok.isNot(tok::r_paren) && Tok.isNot(tok::eof))
-      Lex(Tok);
+    // Skip this token if it's a ')'.
     if (Tok.is(tok::r_paren))
       Lex(Tok);
     return _PragmaLexing.failed();
   }
 
   if (Tok.hasUDSuffix()) {
     Diag(Tok, diag::err_invalid_string_udl);
     // Skip this token, and the ')', if present.

test/Preprocessor/_Pragma.c

 // RUN: %clang_cc1 %s -verify -Wall
 
 _Pragma ("GCC system_header")  // expected-warning {{system_header ignored in main file}}
 
 // rdar://6880630
 _Pragma("#define macro")    // expected-warning {{unknown pragma ignored}}
 
 _Pragma("") // expected-warning {{unknown pragma ignored}}
 _Pragma("message(\"foo \\\\\\\\ bar\")") // expected-warning {{foo \\ bar}}
 
 #ifdef macro
 #error #define invalid
 #endif
 
-_Pragma( // expected-error{{_Pragma takes a parenthesized string literal}}
+// expected-error@+2{{unterminated conditional directive}}
+// expected-error@+1{{expected value in expression}}
+#if _Pragma( // expected-error{{_Pragma takes a parenthesized string literal}}