t5532: workaround for BusyBox on Windows

While it may seem super convenient to some old Unix hands to simpy
require Perl to be available when running the test suite, this is a
major hassle on Windows, where we want to verify that Perl is not,
actually, required in a NO_PERL build.

As a super ugly workaround, we "install" a script into /usr/bin/perl
reading like this:

	#!/bin/sh

	# We'd much rather avoid requiring Perl altogether when testing
	# an installed Git. Oh well, that's why we cannot have nice
	# things.
	exec c:/git-sdk-64/usr/bin/perl.exe "$@"

The problem with that is that BusyBox assumes that the #! line in a
script refers to an executable, not to a script. So when it encounters
the line #!/usr/bin/perl in t5532's proxy-get-cmd, it barfs.

Let's help this situation by simply executing the Perl script with the
"interpreter" specified explicitly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t5532-fetch-proxy.sh

@@ -27,7 +27,7 @@ test_expect_success 'setup proxy script' '
 
 	write_script proxy <<-\EOF
 	echo >&2 "proxying for $*"
-	cmd=$(./proxy-get-cmd)
+	cmd=$("$PERL_PATH" ./proxy-get-cmd)
 	echo >&2 "Running $cmd"
 	exec $cmd
 	EOF