LoongArch: Add support for <b ".L1"> and <beq, $t0, $t1, ".L1">

Support symbol names enclosed in double quotation marks.

gas/testsuite/gas/loongarch/double_quotation_marks.d

@@ -0,0 +1,13 @@
+#as:
+#objdump: -dr
+
+.*:[    ]+file format .*
+
+
+Disassembly of section .text:
+
+.* <.text>:
+[ 	]+0:[ 	]+50000000[ 	]+b[ 	]+0[ 	]+# 0x0
+[ 	]+0: R_LARCH_B26[ 	]+.L1
+[ 	]+4:[ 	]+5800018d[ 	]+beq[ 	]+\$t0, \$t1, 0[ 	]+# 0x4
+[ 	]+4: R_LARCH_B16[ 	]+.L1

gas/testsuite/gas/loongarch/double_quotation_marks.s

@@ -0,0 +1,2 @@
+b ".L1"
+beq $r12, $r13, ".L1"

opcodes/loongarch-coder.c

@@ -264,6 +264,13 @@ loongarch_split_args_by_comma (char *args, const char *arg_strs[])
 	else
 	  *args = '\0', arg_strs[num++] = args + 1;
       }
+
+  if (*(args-1) == '"')
+    {
+      *(args-1) = '\0';
+      arg_strs[num-1] = arg_strs[num-1] + 1;
+    }
+
   arg_strs[num] = NULL;
   return num;
 }