Use uname -m instead of uname -p (#372)

On my Debian machine, uname -p returns "unknown" and the manpage says -p
is non-portable. I do get x86_64 on from uname -m and that doesn't have
the non-portable disclaimer on it.

> Please add a description of your PR.
> If this is a solution to an open challenge, please explain your
solution.
>
> Don't forget to check our book to ensure your solution satisfy the
overall
> requirements as well as the challenge success criteria.
>

Resolves #ISSUE-NUMBER

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

Author: patricklam

scripts/kani-std-analysis/std-analysis.sh

@@ -18,18 +18,18 @@
 set -eu
 
 # Test for platform
-PLATFORM=$(uname -sp)
+PLATFORM=$(uname -sm)
 if [[ $PLATFORM == "Linux x86_64" ]]
 then
   TARGET="x86_64-unknown-linux-gnu"
   # 'env' necessary to avoid bash built-in 'time'
   WRAPPER="env time -v"
-elif [[ $PLATFORM == "Darwin i386" ]]
+elif [[ $PLATFORM == "Darwin x86_64" ]]
 then
   TARGET="x86_64-apple-darwin"
   # mac 'time' doesn't have -v
   WRAPPER="time"
-elif [[ $PLATFORM == "Darwin arm" ]]
+elif [[ $PLATFORM == "Darwin arm64" ]]
 then
   TARGET="aarch64-apple-darwin"
   # mac 'time' doesn't have -v