gdb: fix debug dump of OP_BOOL expressions

gdb: fix debug dump of OP_BOOL expressions

Consider this GDB session:

  (gdb) set language fortran
  (gdb) set debug expression 1
  (gdb) p .TRUE.
  Dump of expression @ 0x4055d90, before conversion to prefix form:
  	Language fortran, 3 elements, 16 bytes each.
  	Index                Opcode         Hex Value  String Value
  	    0               OP_BOOL  79  O...............
  	    1             BINOP_ADD  1  ................
  	    2               OP_BOOL  79  O...............
  Dump of expression @ 0x4055d90, after conversion to prefix form:
  Expression: `TRUE'
  	Language fortran, 3 elements, 16 bytes each.

  	    0  OP_BOOL               Unknown format
  	    1  BINOP_ADD
  	    2    OP_BOOL               Unknown format
  	    3    OP_NULL               Unknown format
  $1 = .TRUE.

The final dump of the OP_BOOL is completely wrong.  After this patch
we now get:

  (gdb) set language fortran
  (gdb) set debug expression 1
  (gdb) p .TRUE.
  Dump of expression @ 0x2d07470, before conversion to prefix form:
  	Language fortran, 3 elements, 16 bytes each.
  	Index                Opcode         Hex Value  String Value
  	    0               OP_BOOL  79  O...............
  	    1             BINOP_ADD  1  ................
  	    2               OP_BOOL  79  O...............
  Dump of expression @ 0x2d07470, after conversion to prefix form:
  Expression: `TRUE'
  	Language fortran, 3 elements, 16 bytes each.

  	    0  OP_BOOL               TRUE
  $1 = .TRUE.

Much better.  I added a test for this into the Fortran testsuite.

gdb/ChangeLog:

	* expprint.c (dump_subexp_body_standard): Handle OP_BOOL.

gdb/testsuite/ChangeLog:

	* gdb.fortran/debug-expr.exp: Add new tests.