tests: use perl's qx!...! rather than ...

* tests/misc/expr: As above.
* tests/misc/ls-misc: Likewise.
* tests/misc/pwd-long: Likewise.
* tests/misc/uniq: Likewise.

tests/misc/expr

@@ -175,7 +175,7 @@ my @Tests =
     );
 
 # If using big numbers fails, remove all /^bignum-/ tests
-`expr $big_prod '*' $big_prod '*' $big_prod`
+qx!expr $big_prod '*' $big_prod '*' $big_prod!
   or @Tests = grep {$_->[0] !~ /^bignum-/} @Tests;
 
 # Append a newline to end of each expected 'OUT' string.

tests/misc/ls-misc

@@ -331,7 +331,7 @@ $fail
   and exit 1;
 
 # Be careful to use the just-build dircolors.
-my $env = `$ENV{abs_top_builddir}/src/dircolors -b`;
+my $env = qx/dircolors -b/;
 $env =~ s/^LS_COLORS=\'//;
 $env =~ s/\';.*//sm;
 $ENV{LS_COLORS} = $env;

tests/misc/pwd-long

@@ -97,7 +97,7 @@ my $pwd_binary = "$build_src_dir/pwd";
 
 -x $pwd_binary
   or die "$ME: $pwd_binary is not an executable file\n";
-chomp (my $actual = `$pwd_binary`);
+chomp (my $actual = qx!$pwd_binary!);
 
 # Convert the absolute name from pwd into a $CWD-relative name.
 # This is necessary in order to avoid a spurious failure when run

tests/misc/uniq

@@ -86,7 +86,7 @@ my $locale = $ENV{LOCALE_FR};
   and CuSkip::skip "$prog: skipping this test -- no appropriate locale\n";
 
 # See if isblank returns true for nbsp.
-my $x = `env printf '\xa0'| LC_ALL=$locale tr '[:blank:]' x`;
+my $x = qx!env printf '\xa0'| LC_ALL=$locale tr '[:blank:]' x!;
 # If so, expect just one line of output in the schar test.
 # Otherwise, expect two.
 my $in = " y z\n\xa0 y z\n";