Also strip leading whitespace from autogen.input lines

...which allows to align --enable/--disable switches on the part being en-/dis-
abled, as in

> --disable-assert-always-abort
>  --enable-avahi
>  --enable-breakpad
>  --enable-build-unowinreg
> --disable-ccache

for better readability

Change-Id: I490402c74ea1ee535deee6ef79274b588b614820
Reviewed-on: https://gerrit.libreoffice.org/48130
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

autogen.sh

@@ -77,6 +77,7 @@ sub read_args($)
     open ($fh, $file) || die "can't open file: $file";
     while (<$fh>) {
         chomp();
+        s/^\s+//;
         s/\s+$//;
         # migrate from the old system
         if ( substr($_, 0, 1) eq "'" ) {