automake: portability fixes

The rework of the host tools discovery caused automake to embed
absolute paths to staging_dir/host/bin/perl into the shebang
of the generated automake executables.

Switch to the portable "/usr/bin/env perl" and enable global
warnings through "$^W" instead of the "-w" interpreter argument.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

SVN-Revision: 44972

tools/automake/patches/100-aclocal-skip-not-existing-directories.patch

@@ -1,6 +1,6 @@
 --- a/bin/aclocal.in
 +++ b/bin/aclocal.in
-@@ -354,6 +354,12 @@ sub scan_m4_dirs ($$@)
+@@ -356,6 +356,12 @@ sub scan_m4_dirs ($$@)
  
    foreach my $m4dir (@dirlist)
      {