LibreOffice Windows installer release build failure

I need to build the Windows installer in order to test some changes to
the installer code. Having had problems building before (last Dec) with
VS2013 I just checked out master and tried to build before making any of 
these amendments.

Build on Windows 7 (32-bit) VM with
Visual Studio 2015 Community (Update 2)
Windows 10 SDK 10586.15
Setup with LODE

make works OK
make test-install works OK
make install FAILS

This fails when merging Microsoft_VC140_CRT_x86.msm.

Here is what seems to me the relevant snippet from the 'make install' log:

: Thu May  5 09:37:24 2016 (00:16 min.)
: ######################################################
: Creating msi database
: ######################################################
: Systemcall: msidb.exe -f
C:\\cygwin\\tmp\\LibreOffice\\\\idt_files\\en-US\\en-US -d
C:\\cygwin\\tmp\\LibreOffice\\\\idt_files\\en-US\\en-US\\libreoffice52_en-US.msi 

-c -i \*
: Success: Executed msidb.exe successfully!
:
: Thu May  5 09:37:25 2016 (00:17 min.)
: ######################################################
: Writing summary information stream
: ######################################################
:
: Thu May  5 09:37:25 2016 (00:17 min.)
: ######################################################
: Generating 1 GUID
: ######################################################
: Systemcall: uuidgen.exe -n1 |
: Success: Executed uuidgen.exe successfully!
: PackageCode: {1035C000-F939-40B3-A767-B44BDAFDFDC8}
: Systemcall: msiinfo.exe
C:/cygwin/tmp/LibreOffice//idt_files/en-US/en-US/libreoffice52_en-US.msi
-g 200 -c 0 -p "Intel;1033" -v {1035C000-F939-40B3-A767-B44BDAFDFDC8} -t
"Installation database" -a "SKS" -j "LibreOffice 5.2" -o "LibreOffice"
-k "Install,MSI" -n "Windows Installer" -u 0 -w 0
: Success: Executed msiinfo.exe successfully!
: Copy:
C:/cygwin/tmp/LibreOffice//idt_files/en-US/en-US/libreoffice52_en-US.msi
to
C:/cygwin/tmp/LibreOffice//install/en-US_inprogress/libreoffice52_en-US.msi
: chmod 664,
C:/cygwin/tmp/LibreOffice//install/en-US_inprogress/libreoffice52_en-US.msi
:
: Created directory: C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules
: Copy:
C:/cygwin/tmp/LibreOffice//install/en-US_inprogress/libreoffice52_en-US.msi
to
C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules/libreoffice52_en-US.msi
: chmod 664,
C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules/libreoffice52_en-US.msi
:
: Thu May  5 09:37:25 2016 (00:17 min.)
: ######################################################
: Merging merge modules into msi database
: ######################################################
:
: Performance Info: MergeModule into msi database, start    Thu May 5
09:37:25 2016 (00:17 min.)
:
: Performance Info: Analyzing MergeModules, start    Thu May  5 09:37:25
2016 (00:17 min.)
: Analyzing all Merge Modules
:
: create_directories: Using C:/cygwin/tmp/ for mergefiles !
:
: Already existing directory, did not create: C:/cygwin/tmp/LibreOffice/
:
: Already existing directory, did not create: C:/cygwin/tmp/LibreOffice//
:
: Created directory: C:/cygwin/tmp/LibreOffice//mergefiles/
:
: Created directory: C:/cygwin/tmp/LibreOffice//mergefiles/en-US/
:
: Created directory:
C:/cygwin/tmp/LibreOffice//mergefiles/en-US/gid_MergeModule_Microsoft_VC140_CRT_x86
: Analyzing Merge Module: Microsoft_VC140_CRT_x86.msm
: Copy: C:/Program Files/Common Files/Merge
Modules/Microsoft_VC140_CRT_x86.msm to
C:/cygwin/tmp/LibreOffice//mergefiles/en-US/gid_MergeModule_Microsoft_VC140_CRT_x86/Microsoft_VC140_CRT_x86.msm
: chmod 664,
C:/cygwin/tmp/LibreOffice//mergefiles/en-US/gid_MergeModule_Microsoft_VC140_CRT_x86/Microsoft_VC140_CRT_x86.msm
: Systemcall: msidb.exe -d Microsoft_VC140_CRT_x86.msm -x
MergeModule.CABinet
: Success: Executed msidb.exe -d Microsoft_VC140_CRT_x86.msm -x
MergeModule.CABinet successfully!
: Systemcall: msidb.exe -d Microsoft_VC140_CRT_x86.msm -f
C:\\cygwin\\tmp\\LibreOffice\\\\mergefiles\\en-US\\gid_MergeModule_Microsoft_VC140_CRT_x86 

-e \*
: Success: Executed msidb.exe -d Microsoft_VC140_CRT_x86.msm -f
C:\\cygwin\\tmp\\LibreOffice\\\\mergefiles\\en-US\\gid_MergeModule_Microsoft_VC140_CRT_x86 

-e \* successfully!
: All Merge Modules successfully analyzed
:
: Performance Info: Analyzing MergeModules, stop    Thu May  5 09:37:25
2016 (00:17 min.)
:
:
: Thu May  5 09:37:25 2016 (00:17 min.)
: ######################################################
: Merging Module: Microsoft_VC140_CRT_x86.msm
: ######################################################
: Copy:
C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules/libreoffice52_en-US.msi 

to
C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules/libreoffice52_en-US.msi.1
: chmod 664,
C:/cygwin/tmp/LibreOffice//idt_files/en-US/mergemodules/libreoffice52_en-US.msi.1
:
: Performance Info: Before merging database    Thu May  5 09:37:25 2016
(00:17 min.)
: Systemcall: msidb.exe -d
C:\\cygwin\\tmp\\LibreOffice\\\\idt_files\\en-US\\mergemodules\\libreoffice52_en-US.msi 

-m
C:\\cygwin\\tmp\\LibreOffice\\\\mergefiles\\en-US\\gid_MergeModule_Microsoft_VC140_CRT_x86\\Microsoft_VC140_CRT_x86.msm
: ERROR: Could not execute msidb.exe -d
C:\\cygwin\\tmp\\LibreOffice\\\\idt_files\\en-US\\mergemodules\\libreoffice52_en-US.msi 

-m
C:\\cygwin\\tmp\\LibreOffice\\\\mergefiles\\en-US\\gid_MergeModule_Microsoft_VC140_CRT_x86\\Microsoft_VC140_CRT_x86.msm 

. Returnvalue: 512!
:
: Moved directory from
C:/cygwin/tmp/LibreOffice//install/en-US_inprogress to
C:/cygwin/tmp/LibreOffice//install/en-US_witherror




The _MergeErrors.idt extracted from the updated MSI is helpfully opaque:

Table    NumRowMergeConflicts
s255    i2
_MergeErrors    Table
_Validation    2


There is no _MergeErrors table in the original MSI (copied as
libreoffice52_en-US.ms.1)

Any ideas?

Regards, Stuart (en_GB l10n maintainer)


--
Stuart Swales