Added rule to ecpg lexer to accept "Unicode surrogate pair in extended quoted

string". This is not really needed because the string gets copied to the output
untranslated anyway, but by adding this rule the lexer stays in sync with the
backend lexer.

src/interfaces/ecpg/preproc/pgc.l

@@ -146,6 +146,7 @@ xeinside		[^\\']+
 xeescape		[\\][^0-7]
 xeoctesc		[\\][0-7]{1,3}
 xehexesc		[\\]x[0-9A-Fa-f]{1,2}
+xeunicode		[\\](u[0-9A-Fa-f]{4}|U[0-9A-Fa-f]{8})
 
 /* C version of hex number */
 xch				0[xX][0-9A-Fa-f]*
@@ -505,6 +506,7 @@ cppline			{space}*#([^i][A-Za-z]*|{if}|{ifdef}|{ifndef}|{import})(.*\\{space})*.
 			}
 <xq,xqc,xn,xus>{xqinside}	{ addlit(yytext, yyleng); }
 <xe>{xeinside}		{ addlit(yytext, yyleng); }
+<xe>{xeunicode}		{ addlit(yytext, yyleng); }
 <xe>{xeescape}  	{ addlit(yytext, yyleng); }
 <xe>{xeoctesc}		{ addlit(yytext, yyleng); }
 <xe>{xehexesc}		{ addlit(yytext, yyleng); }