[Pushed] aarch64: Fix warning in aarch64_ptrue_reg

[Andrew Pinski]

After r15-4579-g9ffcf1f193b477, we get the following warning/error while 
bootstrapping on aarch64:
```
../../gcc/gcc/config/aarch64/aarch64.cc: In function ‘rtx_def* 
aarch64_ptrue_reg(machine_mode, unsigned int)’:
../../gcc/gcc/config/aarch64/aarch64.cc:3643:21: error: comparison of integer 
expressions of different signedness: ‘int’ and ‘unsigned int’ 
[-Werror=sign-compare]
 3643 |   for (int i = 0; i < vl; i++)
      |                   ~~^~~~
```

This changes the type of i to unsigned to match the type of vl.

Pushed as obvious after a bootstrap/test on aarch64-linux-gnu.

gcc/ChangeLog:

        * config/aarch64/aarch64.cc (aarch64_ptrue_reg):

Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
---
 gcc/config/aarch64/aarch64.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index e6d957d275d..7fbe3a7380c 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -3640,10 +3640,10 @@ aarch64_ptrue_reg (machine_mode mode, unsigned int vl)
 
   rtx_vector_builder builder (VNx16BImode, vl, 2);
 
-  for (int i = 0; i < vl; i++)
+  for (unsigned i = 0; i < vl; i++)
     builder.quick_push (CONST1_RTX (BImode));
 
-  for (int i = 0; i < vl; i++)
+  for (unsigned i = 0; i < vl; i++)
     builder.quick_push (CONST0_RTX (BImode));
 
   rtx const_vec = builder.build ();
-- 
2.43.0