[flang] Resolve recent NAG failures better, more clean-up, ready for merge.

Original-commit: flang-compiler/f18@5bc5a317f4
Reviewed-on: https://github.com/flang-compiler/f18/pull/183

flang/lib/parser/grammar.h

@@ -2625,7 +2625,7 @@ TYPE_CONTEXT_PARSER("PRINT statement"_en_US,
         "PRINT" >> format, defaulted("," >> nonemptyList(outputItem))))
 
 // R1215 format -> default-char-expr | label | *
-TYPE_PARSER(construct<Format>(label) ||
+TYPE_PARSER(construct<Format>(label / !"_."_ch) ||
     construct<Format>(defaultCharExpr / !"="_tok) || construct<Format>(star))
 
 // R1216 input-item -> variable | io-implied-do

flang/lib/parser/openmp-grammar.h

@@ -454,7 +454,7 @@ TYPE_PARSER(construct<OpenMPDeclareSimdConstruct>(
     maybe(parenthesized(name)), Parser<OmpClauseList>{}))
 
 // Declarative construct & Threadprivate directive
-TYPE_PARSER(lookAhead(!"!$OMP END"_tok) >> "!$OMP "_tok >>
+TYPE_PARSER(!"!$OMP END"_tok >> "!$OMP "_tok >>
     ("DECLARE REDUCTION" >>
             construct<OpenMPDeclarativeConstruct>(
                 construct<OpenMPDeclarativeConstruct>(
@@ -536,7 +536,7 @@ TYPE_PARSER("PARALLEL SECTIONS" >> construct<OpenMPParallelSectionsConstruct>(
                                        block, Parser<OmpEndParallelSections>{}))
 
 TYPE_CONTEXT_PARSER("OpenMP construct"_en_US,
-    skipStuffBeforeStatement >> "!$OMP "_sptok >> lookAhead(!"END"_tok) >>
+    skipStuffBeforeStatement >> "!$OMP "_sptok >> !"END"_tok >>
         (construct<OpenMPConstruct>(
              indirect(Parser<OpenMPStandaloneConstruct>{})) ||
             construct<OpenMPConstruct>(

flang/lib/parser/stmt-parser.h

@@ -27,7 +27,7 @@ namespace Fortran::parser {
 // end-of-statement markers.
 
 // R611 label -> digit [digit]...
-constexpr auto label{space >> digitString / !"_.edq"_ch};
+constexpr auto label{space >> digitString / spaceCheck};
 
 template<typename PA> inline constexpr auto unterminatedStatement(const PA &p) {
   return skipStuffBeforeStatement >>