Fix implementation of bind(C, name='')

Use the same binding name as we would without the bind(C), so include the
module name in it. This is done by delaying processing of an explicit empty
bind name until routine process_bind to allow that case to be treated
differently from the implicit empty name case.

Also rearrange the code in routine semant1 to reduce the arbitrary
differences in the cases that process the two main bind attribute
reductions.  The processing for the unnamed variant is a subset of
the processing for the named variant, which is now more apparent
in the code.

tools/flang1/flang1exe/semant.c

@@ -7570,16 +7570,17 @@ semant1(int rednum, SST *top)
    *      <bind attr> ::= ( <id name> ) |
    */
   case BIND_ATTR1:
-    /* see also FUNC_SUFFIX2 for a copy of this  processing */
-    np = scn.id.name + SST_CVALG(RHS(2));
+    /* see also FUNC_SUFFIX2 for a copy of this processing */
 
     bind_attr.exist = -1;
     bind_attr.altname = 0;
 
-    if (sem_strcmp(np, "c") == 0) {
-      bind_attr.exist = DA_B(DA_C);
-    } else
+    np = scn.id.name + SST_CVALG(RHS(2));
+    if (sem_strcmp(np, "c") != 0) {
       error(4, 3, gbl.lineno, "Illegal BIND -", np);
+    } else {
+      bind_attr.exist = DA_B(DA_C);
+    }
 
     break;
   /*
@@ -7593,17 +7594,15 @@ semant1(int rednum, SST *top)
 
     bind_attr.exist = -1;
     bind_attr.altname = 0;
+
     np = scn.id.name + SST_CVALG(RHS(2));
     if (sem_strcmp(np, "c") != 0) {
       error(4, 3, gbl.lineno, "Illegal BIND -", np);
     } else {
-      bind_attr.exist = DA_B(DA_C);
-      np = stb.n_base + CONVAL1G(SST_SYMG(RHS(6)));
-      if (*np) {
-        bind_attr.exist |= DA_B(DA_ALIAS);
-        bind_attr.altname = SST_SYMG(RHS(6));
-      }
+      bind_attr.exist = DA_B(DA_C) | DA_B(DA_ALIAS);
+      bind_attr.altname = SST_SYMG(RHS(6)); // altname may be ""
     }
+
     break;
 
   /* ------------------------------------------------------------------ */
@@ -12969,6 +12968,7 @@ process_bind(int sptr)
   int b_type;
   int b_bitv;
   int need_altname = 0;
+  char *np;
   char *w32_name;
   int wsptr;
 
@@ -12991,6 +12991,11 @@ process_bind(int sptr)
 
     switch (b_type) {
     case DA_ALIAS:
+      /* An altname can't be empty.  Exit early to use a "normal" mangled
+       * variant of the primary symbol name. */
+      np = stb.n_base + CONVAL1G(bind_attr.altname);
+      if (!*np)
+        return;
 #if defined(TARGET_OSX)
       /* Win32 and OSX needs altname with underbar for bind only, to
          match C routines.  Do not depend on processing in
@@ -12999,7 +13004,7 @@ process_bind(int sptr)
        */
       w32_name = (char *)getitem(0, strlen(SYMNAME(bind_attr.altname)) + 1);
       w32_name[0] = '_';
-      strcpy(&(w32_name[1]), stb.n_base + CONVAL1G(bind_attr.altname));
+      strcpy(&(w32_name[1]), np);
 
       wsptr = getstring(w32_name, strlen(w32_name));
       ALTNAMEP(sptr, wsptr);