Add some more information about how to compile things for JVM.

Hopefully this'll let NativeCall with the JVM backend compile libs on Windows
platforms.

tools/build/gen-jvm-properties.pl

@@ -31,6 +31,7 @@
 # in the future, I found this to be an invaluable reference:
 # http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/Glossary
 my $ccdlflags = "$Config{cccdlflags} $Config{ccdlflags}";
+my $ldout = $^O eq 'MSWin32'? '-out:' : '-o';
 
 print <<"END";
 # This file automatically generated by $0
@@ -45,6 +46,8 @@
 nativecall.ccflags=$Config{ccflags}
 nativecall.ccdlflags=$ccdlflags
 nativecall.ld=$Config{ld}
+nativecall.ldout=$ldout
 nativecall.ldflags=$Config{ldflags}
 nativecall.lddlflags=$Config{lddlflags}
+nativecall.libs=$Config{libs}
 END