c++: Fix parsing of prefixed C++11 raw string literals

See http://en.cppreference.com/w/cpp/language/string_literal

tagmanager/ctags/get.c

@@ -802,8 +802,12 @@ process:
 					 *
 					 * which is perfectly valid (yet probably very unlikely). */
 					int prev = fileGetNthPrevC (1, 0);
+					int prev2 = fileGetNthPrevC (2, 0);
+					int prev3 = fileGetNthPrevC (3, 0);
 
-					if (! isident (prev))
+					if (! isident (prev) ||
+					    (! isident (prev2) && (prev == 'L' || prev == 'u' || prev == 'U')) ||
+					    (! isident (prev3) && (prev2 == 'u' && prev == '8')))
 					{
 						int next = fileGetc ();
 						if (next != DOUBLE_QUOTE)

tests/ctags/cxx11-raw-strings.cpp

@@ -19,3 +19,16 @@ struct typ2 { int memb2; };
 static const char* str3 = FOUR"f(iv)e";
 
 struct typ3 { int memb3; };
+
+/* check for prefixes */
+static const char* str4 = LR"blah(";int bug4;)blah";
+struct typ4 { int memb4; };
+
+static const char* str5 = u8R"blah(";int bug5;)blah";
+struct typ5 { int memb5; };
+
+static const char* str6 = uR"blah(";int bug6;)blah";
+struct typ6 { int memb6; };
+
+static const char* str7 = UR"blah(";int bug7;)blah";
+struct typ7 { int memb7; };

tests/ctags/cxx11-raw-strings.cpp.tags

@@ -3,9 +3,21 @@ FOUR
 memb164typ10int
 memb264typ20int
 memb364typ30int
+memb464typ40int
+memb564typ50int
+memb664typ60int
+memb764typ70int
 str1163840char
 str2163840char
 str3163840char
+str4163840char
+str5163840char
+str6163840char
+str7163840char
 typ120480
 typ220480
 typ320480
+typ420480
+typ520480
+typ620480
+typ720480