Clean up memory leak warnings from ASAN and Valgrind

* src/main.c (main): Add "sanitize" to .FEATURES if ASAN is enabled.
* src/expand.c (expand_variable_output): Remember "recursive" setting
in case it's changed by the expansion of the variable.
* src/file.c (rehash_file): If we drop a file from the global 'files'
hash, remember it in rehashed_files.  We can't free it because it's
still being referenced (callers will invoke check_renamed()) but
it will be a leak since it's no longer referenced by 'files'.
* src/remake.c (update_file_1): If we drop a dependency, remember it
in dropped_list.  We can't free it because it's still being referenced
by callers but it will be a leak since it's no longer referenced as
a prerequisite.
* tests/scripts/functions/guile: Don't run Guile tests when ASAN is
enabled.
* tests/scripts/functions/wildcard: Enabling ASAN causes glob(3) to
break!  Don't run this test.
* tests/scripts/features/exec: Valgrind's exec() doesn't support
scripts with no shbang.
* tests/scripts/jobserver: Valgrind fails if TMPDIR is set to an
invalid directory: skip those tests.
* tests/scripts/features/output-sync: Ditto.
* tests/scripts/features/temp_stdin: Ditto.

tests/scripts/features/exec

@@ -15,7 +15,11 @@ my $details = "The various shells that this test uses are the default"
 $port_type eq 'UNIX' or return -1;
 $^O =~ /cygwin/ and return -1;
 
-my @shbangs = ('', '#!/bin/sh', "#!$perl_name");
+my @shbangs = ('#!/bin/sh', "#!$perl_name");
+
+# The exec in Valgrind's VM doesn't allow starting commands without any shbang
+$valgrind or push @shbangs, '';
+
 my @shells = ('', 'SHELL=/bin/sh');
 
 # Try whatever shell the user has, as long as it's not a C shell.