[OpenMP] Set pragma start loc to `#pragma` loc

This patch adjusts `PragmaOpenMPHandler` to set the location of
`tok::annot_pragma_openmp` to the `#pragma` location instead of the
`omp` location so that the former becomes the start location of the
OpenMP AST node.  This can be useful when, for example, rewriting a
directive using Clang's Rewrite facility.  Most of this patch updates
tests for changes to locations in diagnostics and `-ast-dump` output.

Reviewed By: ABataev, lebedev.ri, Meinersbur, aaron.ballman

Differential Revision: https://reviews.llvm.org/D61509

llvm-svn: 361867
diff --git a/clang/test/AST/ast-dump-openmp-cancellation-point.c b/clang/test/AST/ast-dump-openmp-cancellation-point.c
index 36baa73..7090090 100644
--- a/clang/test/AST/ast-dump-openmp-cancellation-point.c
+++ b/clang/test/AST/ast-dump-openmp-cancellation-point.c
@@ -10,11 +10,11 @@
 // CHECK: TranslationUnitDecl {{.*}} <<invalid sloc>> <invalid sloc>
 // CHECK: `-FunctionDecl {{.*}} <{{.*}}ast-dump-openmp-cancellation-point.c:3:1, line:8:1> line:3:6 test 'void ()'
 // CHECK-NEXT:   `-CompoundStmt {{.*}} <col:13, line:8:1>
-// CHECK-NEXT:     `-OMPParallelDirective {{.*}} <line:4:9, col:21>
+// CHECK-NEXT:     `-OMPParallelDirective {{.*}} <line:4:1, col:21>
 // CHECK-NEXT:       `-CapturedStmt {{.*}} <line:5:3, line:7:3>
 // CHECK-NEXT:         `-CapturedDecl {{.*}} <<invalid sloc>> <invalid sloc> nothrow
 // CHECK-NEXT:           |-CompoundStmt {{.*}} <line:5:3, line:7:3> openmp_structured_block
-// CHECK-NEXT:           | `-OMPCancellationPointDirective {{.*}} <line:6:9, col:40> openmp_standalone_directive
-// CHECK-NEXT:           |-ImplicitParamDecl {{.*}} <line:4:9> col:9 implicit .global_tid. 'const int *const restrict'
-// CHECK-NEXT:           |-ImplicitParamDecl {{.*}} <col:9> col:9 implicit .bound_tid. 'const int *const restrict'
-// CHECK-NEXT:           `-ImplicitParamDecl {{.*}} <col:9> col:9 implicit __context 'struct (anonymous at {{.*}}ast-dump-openmp-cancellation-point.c:4:9) *const restrict'
+// CHECK-NEXT:           | `-OMPCancellationPointDirective {{.*}} <line:6:1, col:40> openmp_standalone_directive
+// CHECK-NEXT:           |-ImplicitParamDecl {{.*}} <line:4:1> col:1 implicit .global_tid. 'const int *const restrict'
+// CHECK-NEXT:           |-ImplicitParamDecl {{.*}} <col:1> col:1 implicit .bound_tid. 'const int *const restrict'
+// CHECK-NEXT:           `-ImplicitParamDecl {{.*}} <col:1> col:1 implicit __context 'struct (anonymous at {{.*}}ast-dump-openmp-cancellation-point.c:4:1) *const restrict'