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/evalvars.c b/src/evalvars.c
index f787e81..64455f0 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -776,7 +776,7 @@
     cctx_T	*cctx = vim9compile ? eap->cookie : NULL;
     int		count = 0;
 
-    if (eap->getline == NULL)
+    if (eap->ea_getline == NULL)
     {
 	emsg(_(e_cannot_use_heredoc_here));
 	return NULL;
@@ -856,7 +856,7 @@
 	int	ti = 0;
 
 	vim_free(theline);
-	theline = eap->getline(NUL, eap->cookie, 0, FALSE);
+	theline = eap->ea_getline(NUL, eap->cookie, 0, FALSE);
 	if (theline == NULL)
 	{
 	    semsg(_(e_missing_end_marker_str), marker);