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/userfunc.c b/src/userfunc.c
index 1580a37..ea03e78 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -198,10 +198,10 @@
 {
     char_u *theline;
 
-    if (eap->getline == NULL)
+    if (eap->ea_getline == NULL)
 	theline = getcmdline(':', 0L, indent, 0);
     else
-	theline = eap->getline(':', eap->cookie, indent, getline_options);
+	theline = eap->ea_getline(':', eap->cookie, indent, getline_options);
     if (theline != NULL)
     {
 	if (lines_to_free->ga_len > 0
@@ -264,7 +264,7 @@
     p = arg;
     while (*p != endchar)
     {
-	while (eap != NULL && eap->getline != NULL
+	while (eap != NULL && eap->ea_getline != NULL
 			 && (*p == NUL || (VIM_ISWHITE(*whitep) && *p == '#')))
 	{
 	    // End of the line, get the next one.
@@ -889,7 +889,7 @@
 
     // Detect having skipped over comment lines to find the return
     // type.  Add NULL lines to keep the line count correct.
-    sourcing_lnum_off = get_sourced_lnum(eap->getline, eap->cookie);
+    sourcing_lnum_off = get_sourced_lnum(eap->ea_getline, eap->cookie);
     if (SOURCING_LNUM < sourcing_lnum_off)
     {
 	sourcing_lnum_off -= SOURCING_LNUM;
@@ -952,7 +952,7 @@
 	}
 
 	// Detect line continuation: SOURCING_LNUM increased more than one.
-	sourcing_lnum_off = get_sourced_lnum(eap->getline, eap->cookie);
+	sourcing_lnum_off = get_sourced_lnum(eap->ea_getline, eap->cookie);
 	if (SOURCING_LNUM < sourcing_lnum_off)
 	    sourcing_lnum_off -= SOURCING_LNUM;
 	else
@@ -1349,7 +1349,7 @@
 	fill_exarg_from_cctx(&eap, evalarg->eval_cctx);
     else
     {
-	eap.getline = evalarg->eval_getline;
+	eap.ea_getline = evalarg->eval_getline;
 	eap.cookie = evalarg->eval_cookie;
     }