[OpenCL] Allow pipe as a valid identifier prior to OpenCL 2.0

[Anastasia]

Summary

pipe has not been a reserved keyword in the earlier OpenCL standards
https://www.khronos.org/registry/OpenCL/specs/opencl-1.2.pdf
however we failed to allow its use as an identifier in the original implememntation.

This patch fixes the issue and improves testing.

Btw I feel we have a spec issue in the unified spec https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_C.html#keywords because it doesn't say that the pipe is reserved only from OpenCL 2.0?
I have created this for clarifications: https://github.com/KhronosGroup/OpenCL-Docs/issues/601

[svenvh]

LGTM

clang/lib/Parse/ParseDecl.cpp

case tok::kw___bool:
       isInvalid = DS.SetTypeAltiVecBool(true, Loc, PrevSpec, DiagID, Policy);
       break;
     case tok::kw_pipe:
       if (!getLangOpts().OpenCL || (getLangOpts().OpenCLVersion < 200 &&
                                     !getLangOpts().OpenCLCPlusPlus)) {
         // OpenCL 2.0 and later define this keyword. OpenCL 1.2 and earlier
         // should support the "pipe" word as identifier.
         Tok.getIdentifierInfo()->revertTokenIDToIdentifier();
+        Tok.setKind(tok::identifier);
         goto DoneWithDeclSpec;
       }
       isInvalid = DS.SetTypePipe(true, Loc, PrevSpec, DiagID, Policy);
       break;
 // We only need to enumerate each image type once.
 #define IMAGE_READ_WRITE_TYPE(Type, Id, Ext)
 #define IMAGE_WRITE_TYPE(Type, Id, Ext)
 #define IMAGE_READ_TYPE(ImgType, Id, Ext) \

clang/test/SemaOpenCL/invalid-pipes-cl1.2.cl

 // RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only -cl-std=CL1.2
 
-void foo(read_only pipe int p); // expected-error {{expected parameter declarator}} expected-error {{expected ')'}} expected-note {{to match this '('}}
+void foo(read_only pipe int p);
+// expected-warning@-1 {{type specifier missing, defaults to 'int'}}
+// expected-error@-2 {{access qualifier can only be used for pipe and image type}}
+// expected-error@-3 {{expected ')'}} expected-note@-3 {{to match this '('}}
+
+// 'pipe' should be accepted as an identifier.
+typedef int pipe;