Ensure that libraries link to the shared version of NTL by default

[kcrisman]

In #11547, we added copying of several needed dlls on Cygwin. However, in the meantime NTL had a fairly major update (#5731).

From version 5.5, NTL provides a new build system using libtool (although libtool itself is not provided!) to generate shared libraries.
On Cygwin, libtool properly install the shared library as cygntl-?.dll in the bin directory and the import file as libntl.dll.a in the lib directory, together with a libtool file libntl.la and a static version of the library as libntl.a.

In particular, this ensures that the shared version is linked with by default because ld/gcc/g++ find the .dll.a file in the lib directory (which points to the dll file in the bin directory) before the .a file.

Moreover, only moving the previously built libntl.dll to libntl.dll.a was not a solution.
Indeed, the built file hardcoded its own build-time name into itself (as a DT_SONAME on linux), so that libraries linked to it (before or after renaming, does not matter) would in fact search for a file with the build time name... and fail.

spkg: http://boxen.math.washington.edu/home/jdemeyer/spkg/ntl-5.5.2.p0.spkg

This spkg vastly simplifies the old spkg-install, uses the (slightly patched) upstream build system and includes its own version of libtool (or rather the tools needed to generate it on the fly).

CC: @mwhansen @dimpase @jpflori @jdemeyer

Component: porting: Cygwin

Keywords: cygwin ntl libtool spkg

Author: Jean-Pierre Flori

Reviewer: Karl-Dieter Crisman

Merged: sage-5.6.beta3

Issue created by migration from https://trac.sagemath.org/ticket/11635

[kcrisman]

Description changed:

--- 
+++ 
@@ -1,6 +1,8 @@
 In #11547, we added copying of several needed dlls on Cygwin.  However, in the meantime NTL had a fairly major update (#5731).
 
 Based on this, this ticket splits off the NTL change from #11547 so that that ticket can get merged.  
+
+Spkg at [http://sage.math.washington.edu/home/kcrisman/ntl-5.5.2.p0.spkg](http://sage.math.washington.edu/home/kcrisman/ntl-5.5.2.p0.spkg).
 
 Here is the previous diff - presumably we would do the same thing if we can confirm it is still necessary, which is almost certainly the case.
 

[kcrisman]

comment:1

New spkg at http://sage.math.washington.edu/home/kcrisman/ntl-5.5.2.p0.spkg. No guarantees on whether this works, or even is necessary (!) but I strongly suspect both. You'll know it works if you do everything at #6743, including this, and then Sage has a segfault on startup.

In case there is any doubt that this is Cygwin-only:

    elif [ $UNAME = "CYGWIN" ]; then
        # Cygwin
        if [ "$CYGPKG" = "yes" ]; then
            if [ -f /lib/libgmp.dll.a ]; then
                ln -s /lib/libgmp.dll.a libgmp.a
            else
                # Added by William Stein on 2006-02-06 so that 
                # can build even if gmp is not built locally
                # i.e., even if using a system-wide gmp.
                # (though it has to be in /usr/lib, which is
                # where it is for cygwin).
                ln  -s /usr/lib/*gmp* .
                ln  -s libgmp.dll.a libgmp.a
            fi 
        else
   	    ln -s "$SAGE_LOCAL/lib/libgmp.a" .
        fi
	$MAKE libntl.dll
        if [ ! -f libntl.dll ]; then
            echo "Error creating ntl shared library."
            exit 1
        fi
	cp libntl.dll "$SAGE_LOCAL/lib/libntl.dll.a"
	cp libntl.dll "$SAGE_LOCAL/lib/libntl.dll"
	cp libntl.dll "$SAGE_LOCAL/bin/libntl.dll.a"
	cp libntl.dll "$SAGE_LOCAL/bin/libntl.dll"
        if [ ! -f "$SAGE_LOCAL/bin/libntl.dll.a" ]; then
            exit 1   # CRUCIAL that we have the dynamic link library
        fi

[kcrisman]

Author: Karl-Dieter Crisman

[kcrisman]

comment:3

Interestingly, the most recent alpha I tested all the Cygwin stuff on a few weeks ago already had NTL 5.5.2!

$ ls spkg/installed
<snip>
ntl-5.5.2
<snip>

and it seemed to work fine (in the sense that it got to the Pari segfault when initializing).

That doesn't mean that later in the process things wouldn't happen, but at least for now this ticket can be lower priority, if it's needed at all, since we have to figure out how to get past that error first.

[kcrisman]

comment:5

This appears to be the same issue as #12104, which should probably be closed as a duplicate then.

[kcrisman]

comment:6

Since the 4.8.alpha3 spkg still is 5.5.2 with no patches, this spkg should still be valid to fix this.