Error when trying --enable-lto on Windows

Anybody care to guess what might cause this?

   Creating library
C:/cygwin64/home/Tor/lo/master/workdir/LinkTarget/Library/ifwk.lib and
object C:/cygwin64/home/Tor/lo/master/workdir/LinkTarget/Library/ifwk.exp
modulemanager.o : error LNK2001: unresolved external symbol
"__declspec(dllimport) public: virtual class com::sun::star::uno::Any
__cdecl cppu::WeakImplHelper<class
com::sun::star::container::XEnumeration>::queryInterface(class
com::sun::star::uno::Type const &)" (__imp_?queryInterface@
?$WeakImplHelper@VXEnumeration@container@star@sun@com@@@cppu@@UAA?AVAny@uno
@star@sun@com@@ABVType@4567@@Z)
modulemanager.o : error LNK2001: unresolved external symbol
"__declspec(dllimport) public: virtual void __cdecl
cppu::WeakImplHelper<class
com::sun::star::container::XEnumeration>::acquire(void)" (__imp_?acquire@
?$WeakImplHelper@VXEnumeration@container@star@sun@com@@@cppu@@UAAXXZ)
modulemanager.o : error LNK2001: unresolved external symbol
"__declspec(dllimport) public: virtual void __cdecl
cppu::WeakImplHelper<class
com::sun::star::container::XEnumeration>::release(void)" (__imp_?release@
?$WeakImplHelper@VXEnumeration@container@star@sun@com@@@cppu@@UAAXXZ)
C:/cygwin64/home/Tor/lo/master/instdir/program/fwklo.dll : fatal error
LNK1120: 3 unresolved externals

This is with a very simple autogen.input:

--disable-odk
--without-java
--enable-lto

Lots of other DLLs have already been built successfully, so it is not some
general problem with using LTO.

--tml