Fix c_check misinterpreting arm64 in uname output to mean armv7

additionla fix for upcoming OSX on ARM64 related to #2804, as suggested by fxcoudert in #2805

c_check

@@ -8,7 +8,7 @@ $hostos   = `uname -s | sed -e s/\-.*//`;    chop($hostos);
 $hostarch = `uname -m | sed -e s/i.86/x86/`;chop($hostarch);
 $hostarch = `uname -p` if ($hostos eq "AIX");
 $hostarch = "x86_64" if ($hostarch eq "amd64");
-$hostarch = "arm" if ($hostarch =~ /^arm.*/);
+$hostarch = "arm" if ($hostarch ne "arm64" && $hostarch =~ /^arm.*/);
 $hostarch = "arm64" if ($hostarch eq "aarch64");
 $hostarch = "power" if ($hostarch =~ /^(powerpc|ppc).*/);
 $hostarch = "zarch" if ($hostarch eq "s390x");