Firebird broke my build

I'm unable to build LO with the latest Firebird update on Windows.

Namely, after this:

commit 288e005ef7ed5b931935da2e1266b95fc9f16cdf
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Mon Jul 13 11:32:17 2015 +0100

    Revert "Revert "Update firebird to version 2.5.4""

    This reverts commit 69632c9c3291a7bb9d465495943aa1dbe12c5af2.

    Change-Id: I4704c30ade878b9e62ac829b03648f301534b51c
    Reviewed-on: https://gerrit.libreoffice.org/16986
    Tested-by: Jenkins <ci@libreoffice.org>
    Reviewed-by: Caolán McNamara <caolanm@redhat.com>
    Tested-by: Caolán McNamara <caolanm@redhat.com>


I bisected to this commit, and can see that Jenkins was able to build it.
However, I see important differences between my build log and on Jenkins.
Specifically, this is what I have:

[snip Firebird configure output]
The Firebird2 package has been configured with the following options:

                   Architecture : ClassicServer
                          Debug : enabled
                    Raw devices : disabled
                   Service name : gds_db
                   Service port : 3050
                      Pipe name : interbas
                   GPRE modules : c_cxx.cpp

                    Install Dir : /usr/local/firebird

make64_41[2]: Entering directory
'C:/prj/libro/libo/workdir/UnpackedTarball/firebird'
C:/Bin/cygwin64/opt/lo/bin/make64_41 -C gen firebird_embedded
make64_41[3]: Entering directory
'C:/prj/libro/libo/workdir/UnpackedTarball/firebird/gen'
C:/Bin/cygwin64/opt/lo/bin/make64_41 -C ../extern/btyacc
make64_41[4]: Entering directory
'C:/prj/libro/libo/workdir/UnpackedTarball/firebird/extern/btyacc'
C:/prj/libro/libo/workdir/LinkTarget/Executable/*gcc-wrapper.exe -o
btyacc.exe closure.o error.o lalr.o lr0.o main.o mkpar.o output.o mstring.o
reader.o readskel.o skeleton.o symtab.o verbose.o warshall.o*
cl : Command line warning D9024 : unrecognized source file type
'closure.o', object file assumed
cl : Command line warning D9024 : unrecognized source file type 'error.o',
object file assumed
cl : Command line warning D9024 : unrecognized source file type 'lalr.o',
object file assumed
cl : Command line warning D9024 : unrecognized source file type 'lr0.o',
object file assumed
...
...

I can't find "Firebird2" in the Jenkins output. I can't find Firebird
configure output either. My build shows a clearly incorrect invocation of
gcc-wrapper, which goes downhill thereafter.
I also have a bunch of "find: `FC:': No such file or directory" lines.

I'm *not* using LODE. I'm building the 32-bit version, with debug-utils.
Clean builds didn't help.

*Any ideas what's going on, and what I'm missing?*

Thanks in advance!