LoongArch: gas: add support using variable for li.w/d

        Macro instruction li.w/d support using variable
        like ".equ var, 123    li.w/d resgister, var".
        Add two testcases.

gas/
        * config/loongarch-parse.y
        * testsuite/gas/loongarch/li.d
        * testsuite/gas/loongarch/li.s
        * testsuite/gas/loongarch/li2.d
        * testsuite/gas/loongarch/li2.s

gas/config/loongarch-parse.y

@@ -100,6 +100,23 @@ my_getExpression (expressionS *ep, const char *str)
   return ret;
 }
 
+/* op is var name?  */
+static void
+emit_const_var (const char *op)
+{
+  expressionS ep;
+  if (end <= top)
+    as_fatal (_("expr too huge"));
+  my_getExpression(&ep, op);
+  if (ep.X_op != O_constant)
+    as_bad("illegal operand: %s", op);
+  top->value.X_op = O_constant;
+  top->value.X_add_number = ep.X_add_number;
+  top->type = BFD_RELOC_LARCH_SOP_PUSH_ABSOLUTE;
+  top++;
+}
+
+
 static void
 reloc (const char *op_c_str, const char *id_c_str, offsetT addend)
 {
@@ -318,6 +335,7 @@ offsetT imm;
 
 primary_expression
 	: INTEGER {emit_const ($1);}
+	| IDENTIFIER {emit_const_var ($1);}
 	| '(' expression ')'
 	| '%' IDENTIFIER '(' IDENTIFIER addend ')' {reloc ($2, $4, $5); free ($2); free ($4);}
 	| '%' IDENTIFIER '(' INTEGER addend ')' {reloc ($2, NULL, $4 + $5); free ($2);}

gas/testsuite/gas/loongarch/li.d

@@ -0,0 +1,14 @@
+#as:
+#objdump: -dr
+
+.*:[    ]+file format .*
+
+
+Disassembly of section .text:
+
+00000000.* <.text>:
+[ 	]+0:[ 	]+03848c0c[ 	]+ori[ 	]+\$t0,[ 	]+\$zero,[ 	]+0x123
+[ 	]+4:[ 	]+15ffe00d[ 	]+lu12i.w[ 	]+\$t1,[ 	]+-256\(0xfff00\)
+[ 	]+8:[ 	]+16001fed[ 	]+lu32i.d[ 	]+\$t1,[ 	]+255\(0xff\)
+[ 	]+c:[ 	]+02bffc0e[ 	]+addi.w[ 	]+\$t2,[ 	]+\$zero,[ 	]+-1\(0xfff\)
+[ 	]+10:[ 	]+1601ffee[ 	]+lu32i.d[ 	]+\$t2,[ 	]+4095\(0xfff\)

gas/testsuite/gas/loongarch/li.s

@@ -0,0 +1,7 @@
+.equ a, 0x123
+.equ b, 0xfffff00000
+.equ c, 0xfffffffffff
+
+li.w $r12, a
+li.d $r13, b
+li.d $r14, c

gas/testsuite/gas/loongarch/li2.d

@@ -0,0 +1,20 @@
+#as:
+#objdump: -dr
+
+.*:[    ]+file format .*
+
+
+Disassembly of section .text:
+
+00000000.* <_start>:
+[ 	]+0:[ 	]+03803c06[ 	]+ori[ 	]+\$a2,[ 	]+\$zero,[ 	]+0xf
+[ 	]+4:[ 	]+1a000005[ 	]+pcalau12i[ 	]+\$a1,[ 	]+0
+[ 	]+4:[ 	]+R_LARCH_PCALA_HI20[ 	]+.rodata
+[ 	]+8:[ 	]+02c000a5[ 	]+addi.d[ 	]+\$a1,[ 	]+\$a1,[ 	]+0
+[ 	]+8:[ 	]+R_LARCH_PCALA_LO12[ 	]+.rodata
+[ 	]+c:[ 	]+03800404[ 	]+ori[ 	]+\$a0,[ 	]+\$zero,[ 	]+0x1
+[ 	]+10:[ 	]+0381000b[ 	]+ori[ 	]+\$a7,[ 	]+\$zero,[ 	]+0x40
+[ 	]+14:[ 	]+002b0000[ 	]+syscall[ 	]+0x0
+[ 	]+18:[ 	]+00150004[ 	]+move[ 	]+\$a0,[ 	]+\$zero
+[ 	]+1c:[ 	]+0381740b[ 	]+ori[ 	]+\$a7,[ 	]+\$zero,[ 	]+0x5d
+[ 	]+20:[ 	]+002b0000[ 	]+syscall[ 	]+0x0

gas/testsuite/gas/loongarch/li2.s

@@ -0,0 +1,22 @@
+.equ EXIT_SUCCESS, 0
+.equ STDOUT, 1
+.equ SYS_exit, 93
+.equ SYS_write, 64
+
+.section .rodata
+msg:
+    .string "hello, world!\n"
+    len = . - msg
+
+.text
+    .globl  _start
+_start:
+    li.w        $a2, len
+    la.local    $a1, msg
+    li.w        $a0, STDOUT
+    li.w        $a7, SYS_write
+    syscall     0x0
+
+    li.w        $a0, EXIT_SUCCESS
+    li.w        $a7, SYS_exit
+    syscall     0x0