Do not do macro expansion on preprocessor directive names.

According to the C standards (C17 section 6.10.3 p8), they should not be subject to macro replacement.

A similar change also applies to the "STDC" in #pragma STDC ... (but we still allow macros for other pragmas, which is allowed as part of the implementation-defined behavior of #pragma).

Here is an example affected by this issue:

#define ifdef ifndef
#ifdef foobar
#error "foobar defined?"
#else
int main(void) {}
#endif

Scanner.pas

@@ -3215,7 +3215,9 @@ nextLineNumber := -1;
 while charKinds[ord(ch)] = ch_white do  {skip white space}
    NextCh;
 if ch in ['a','d','e','i','l','p','u','w'] then begin
+   expandMacros := false;
    NextToken;
+   expandMacros := true;
    case token.kind of
       ifsy: begin
          if not tSkipping then
@@ -3327,12 +3329,19 @@ if ch in ['a','d','e','i','l','p','u','w'] then begin
             'p':
                if token.name^ = 'pragma' then begin
                   if tskipping then goto 2;
+                  expandMacros := false;
                   NextToken;
+                  expandMacros := true;
                   if token.class <> identifier then begin
                      if (lint & lintPragmas) <> 0 then
                         Error(110);
                      goto 2;
                      end; {if}
+                  if token.name^ <> 'STDC' then begin
+                     {Allow macro expansion, other than for STDC   }
+                     PutBackToken(token, true);
+                     NextToken;
+                     end; {if}
                   if token.name^ = 'keep' then
                      DoKeep
                   else if token.name^ = 'debug' then begin

cc.notes

@@ -1946,6 +1946,8 @@ int foo(int[42]);
 
 215. The digit sequence in the #line directive should be interpreted as a decimal number (not octal) even if it begins with a 0.
 
+216. Preprocessing directive names could be subject to macro replacement, potentially altering their behavior (e.g. due to a definition like "#define ifdef ifndef").  Now directive names are not expanded as macros, even if there is a macro of the same name.
+
 -- Bugs from C 2.1.0 that have been fixed -----------------------------------
 
 1.  In some situations, fread() reread the first 1K or so of the file.