patch 8.2.3787: no proper formatting of a C line comment after a statement

Problem:    No proper formatting of a C line comment after a statement.
Solution:   Find the start of the line comment, insert the comment leader and
            indent the comment properly.
diff --git a/src/proto/search.pro b/src/proto/search.pro
index a6843a0..27c609e 100644
--- a/src/proto/search.pro
+++ b/src/proto/search.pro
@@ -29,6 +29,7 @@
 int searchc(cmdarg_T *cap, int t_cmd);
 pos_T *findmatch(oparg_T *oap, int initc);
 pos_T *findmatchlimit(oparg_T *oap, int initc, int flags, int maxtravel);
+int check_linecomment(char_u *line);
 void showmatch(int c);
 int current_search(long count, int forward);
 int linewhite(linenr_T lnum);