patch 8.0.0431: 'cinoptions' cannot set indent for extern block

Problem:    'cinoptions' cannot set indent for extern block.
Solution:   Add the "E" flag in 'cinoptions'. (Hirohito Higashi)
diff --git a/src/misc1.c b/src/misc1.c
index ec92f03..c6b8d13 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -5810,6 +5810,54 @@
 }
 
 /*
+ * Recognize a `extern "C"` or `extern "C++"` linkage specifications.
+ */
+    static int
+cin_is_cpp_extern_c(char_u *s)
+{
+    char_u	*p;
+    int		has_string_literal = FALSE;
+
+    s = cin_skipcomment(s);
+    if (STRNCMP(s, "extern", 6) == 0 && (s[6] == NUL || !vim_iswordc(s[6])))
+    {
+	p = cin_skipcomment(skipwhite(s + 6));
+	while (*p != NUL)
+	{
+	    if (vim_iswhite(*p))
+	    {
+		p = cin_skipcomment(skipwhite(p));
+	    }
+	    else if (*p == '{')
+	    {
+		break;
+	    }
+	    else if (p[0] == '"' && p[1] == 'C' && p[2] == '"')
+	    {
+		if (has_string_literal)
+		    return FALSE;
+		has_string_literal = TRUE;
+		p += 3;
+	    }
+	    else if (p[0] == '"' && p[1] == 'C' && p[2] == '+' && p[3] == '+'
+		    && p[4] == '"')
+	    {
+		if (has_string_literal)
+		    return FALSE;
+		has_string_literal = TRUE;
+		p += 5;
+	    }
+	    else
+	    {
+		return FALSE;
+	    }
+	}
+	return has_string_literal ? TRUE : FALSE;
+    }
+    return FALSE;
+}
+
+/*
  * Return a pointer to the first non-empty non-comment character after a ':'.
  * Return NULL if not found.
  *	  case 234:    a = b;
@@ -6652,6 +6700,7 @@
 {
     char_u	*line;
     char_u	*p;
+    char_u	*new_p;
 
     p = line = ml_get(trypos->lnum);
     while (*p && (colnr_T)(p - line) < trypos->col)
@@ -6660,8 +6709,11 @@
 	    p = cin_skipcomment(p);
 	else
 	{
-	    p = skip_string(p);
-	    ++p;
+	    new_p = skip_string(p);
+	    if (new_p == p)
+		++p;
+	    else
+		p = new_p;
 	}
     }
     return (int)(p - line);
@@ -6977,6 +7029,9 @@
     /* indentation for # comments */
     buf->b_ind_hash_comment = 0;
 
+    /* Handle C++ extern "C" or "C++" */
+    buf->b_ind_cpp_extern_c = 0;
+
     for (p = buf->b_p_cino; *p; )
     {
 	l = p++;
@@ -7051,6 +7106,7 @@
 	    case '#': buf->b_ind_hash_comment = n; break;
 	    case 'N': buf->b_ind_cpp_namespace = n; break;
 	    case 'k': buf->b_ind_if_for_while = n; break;
+	    case 'E': buf->b_ind_cpp_extern_c = n; break;
 	}
 	if (*p == ',')
 	    ++p;
@@ -7764,6 +7820,8 @@
 		    l = skipwhite(ml_get_curline());
 		    if (cin_is_cpp_namespace(l))
 			amount += curbuf->b_ind_cpp_namespace;
+		    else if (cin_is_cpp_extern_c(l))
+			amount += curbuf->b_ind_cpp_extern_c;
 		}
 		else
 		{
@@ -7990,6 +8048,12 @@
 							    - added_to_amount;
 				break;
 			    }
+			    else if (cin_is_cpp_extern_c(l))
+			    {
+				amount += curbuf->b_ind_cpp_extern_c
+							    - added_to_amount;
+				break;
+			    }
 
 			    if (cin_nocode(l))
 				continue;