runtime(erlang): recognize -if/-elif as erlangPreCondit in syntax script

The -if(Condition)/-elif(Condition) are compiler macros that evaluate
the following lines only if Condition evaluates to true.  This patch
enables syntax highlighting for these macros.

https://www.erlang.org/doc/system/macros.html#conditional-compilation

closes: #18729

Signed-off-by: Vadim Yanitskiy <[email protected]>
Signed-off-by: Csaba Hoch <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: fixeria

runtime/syntax/erlang.vim

@@ -3,7 +3,7 @@
 " Maintainer:   Csaba Hoch <[email protected]>
 " Contributor:  Adam Rutkowski <[email protected]>
 "               Johannes Christ <[email protected]>
-" Last Update:  2025-Jul-06
+" Last Update:  2025-Nov-12
 " License:      Vim license
 " URL:          https://github.com/vim-erlang/vim-erlang-runtime
 
@@ -217,7 +217,7 @@ syn match erlangInnerDocAttribute '^\s*-\%(\s\|\n\|%.*\n\)*\%(moduledoc\|doc\)\>
 syn match erlangInclude   '^\s*-\%(\s\|\n\|%.*\n\)*\%(include\|include_lib\)\>' contains=erlangComment
 syn match erlangRecordDef '^\s*-\%(\s\|\n\|%.*\n\)*record\>' contains=erlangComment
 syn match erlangDefine    '^\s*-\%(\s\|\n\|%.*\n\)*\%(define\|undef\)\>' contains=erlangComment
-syn match erlangPreCondit '^\s*-\%(\s\|\n\|%.*\n\)*\%(ifdef\|ifndef\|else\|endif\)\>' contains=erlangComment
+syn match erlangPreCondit '^\s*-\%(\s\|\n\|%.*\n\)*\%(ifdef\|ifndef\|else\|if\|elif\|endif\)\>' contains=erlangComment
 syn match erlangType      '^\s*-\%(\s\|\n\|%.*\n\)*\%(spec\|type\|opaque\|nominal\|callback\)\>' contains=erlangComment
 
 " Keywords