patch 9.0.2180: POSIX function name in exarg causes issues

Problem:  POSIX function name in exarg struct causes issues
          on OpenVMS
Solution: Rename getline member in exarg struct to ea_getline,
          remove isinf() workaround for VMS

There are compilers that do not treat well POSIX functions - like
getline - usage in the structs.

Older VMS compilers could digest this... but the newer OpenVMS compilers
( like VSI C x86-64 X7.4-843 (GEM 50XB9) ) cannot deal with these
structs. This could be limited to getline() that is defined via
getdelim() and might not affect all POSIX functions in general - but
avoiding POSIX function names usage in the structs is a "safe side"
practice without compromising the functionality or the code readability.

The previous OpenVMS X86 port used a workaround limiting the compiler
capabilities using __CRTL_VER_OVERRIDE=80400000
In order to make the OpenVMS port future proof, this pull request
proposes a possible solution.

closes: #13704

Signed-off-by: Zoltan Arpadffy <zoltan.arpadffy@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/usercmd.c b/src/usercmd.c
index 3191257..04b3419 100644
--- a/src/usercmd.c
+++ b/src/usercmd.c
@@ -1110,7 +1110,7 @@
     char_u *retp = p;
 
     if (*p == '{' && ends_excmd2(eap->arg, skipwhite(p + 1))
-						       && eap->getline != NULL)
+						    && eap->ea_getline != NULL)
     {
 	garray_T    ga;
 	char_u	    *line = NULL;
@@ -1127,7 +1127,7 @@
 	    for (;;)
 	    {
 		vim_free(line);
-		if ((line = eap->getline(':', eap->cookie,
+		if ((line = eap->ea_getline(':', eap->cookie,
 					   0, GETLINE_CONCAT_CONTBAR)) == NULL)
 		{
 		    emsg(_(e_missing_rcurly));
@@ -1955,7 +1955,7 @@
 #endif
     }
 
-    (void)do_cmdline(buf, eap->getline, eap->cookie,
+    (void)do_cmdline(buf, eap->ea_getline, eap->cookie,
 				   DOCMD_VERBOSE|DOCMD_NOWAIT|DOCMD_KEYTYPED);
 
     // Careful: Do not use "cmd" here, it may have become invalid if a user