Fix print_multilib_info when default arguments appear in the option list with '!'

This issue is found when we try to always define MULTILIB_DEFAULTS for -march
and -mabi for RISC-V back-end, however `-print-multi-lib` will skip
multi-lib setting if match any one of flag in MULTILIB_DEFAULTS, even
some options are specified in the option list with '!'.

e.g.

We have default march=rv32i and mabi=ilp32.

And we have following multi-lib set:

". !march=rv32i !march=rv32im !march=rv32imafc !mabi=ilp32 !mabi=ilp32f;"
"rv32i/ilp32 march=rv32i !march=rv32im !march=rv32imafc mabi=ilp32 !mabi=ilp32f;"
"rv32im/ilp32 !march=rv32i march=rv32im !march=rv32imafc mabi=ilp32 !mabi=ilp32f;"
"rv32imafc/ilp32f !march=rv32i !march=rv32ic !march=rv32im march=rv32imafc !mabi=ilp32 mabi=ilp32f;"

`-print-multi-lib` willl show `.` and `rv32imafc/ilp32f` only, because
the mabi=ilp32 is matched, however there is `!march=rv32i` in `rv32im/ilp32`, so
`rv32im/ilp32` should keep, because it reject march=rv32i.

Note: This can be reproduced via following configure options with patch [1]:
gcc/configure --target=riscv64-elf --with-arch=rv32i --with-abi=ilp32 \
  --with-multilib-generator="rv32i-ilp32--;rv32im-ilp32--;rv32imafc-ilp32f--"

[1] https://gcc.gnu.org/pipermail/gcc-patches/2020-November/559707.html

gcc/ChangeLog:

	* gcc.c (print_multilib_info): Check default arguments not
	appeared in multi-lib option list with '!'

1 files changed, 17 insertions, 6 deletions

diff --git a/gcc/gcc.c b/gcc/gcc.c
index 16a6ee5..bd4ad3b 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -9775,6 +9775,7 @@ print_multilib_info (void)
   const char *p = multilib_select;
   const char *last_path = 0, *this_path;
   int skip;
+  int not_arg;
   unsigned int last_path_len = 0;
 
   while (*p != '\0')
@@ -9929,9 +9930,13 @@ print_multilib_info (void)
 		goto invalid_select;
 
 	      if (*q == '!')
-		arg = NULL;
+		{
+		  not_arg = 1;
+		  q++;
+		}
 	      else
-		arg = q;
+		not_arg = 0;
+	      arg = q;
 
 	      while (*q != ' ' && *q != ';')
 		{
@@ -9940,11 +9945,17 @@ print_multilib_info (void)
 		  ++q;
 		}
 
-	      if (arg != NULL
-		  && default_arg (arg, q - arg))
+	      if (default_arg (arg, q - arg))
 		{
-		  skip = 1;
-		  break;
+		  /* Stop checking if any default arguments appeared in not
+		     list.  */
+		  if (not_arg)
+		    {
+		      skip = 0;
+		      break;
+		    }
+		  else
+		    skip = 1;
 		}
 
 	      if (*q == ' ')