skip the python KillPython step so two windows builds don't race over it

KillPython runs an inline CodeTaskFactory task that compiles a temporary
dll and loads it. Two parallel builds on one machine race over that dll,
and one build fails to find it:

  pyproject.props(176,5): error MSB4175: The task factory "CodeTaskFactory"
  could not be loaded from the assembly "...\Microsoft.Build.Tasks.Core.dll".
  Could not find file '...\tmp\rmlsuizu\rmlsuizu.dll'.

KillPython only kills a stray python.exe that holds the output file open
across an incremental rebuild. A clean build has none to kill, so pass
/p:KillPython=false to override pythoncore.vcxproj and skip the target.

Signed-off-by: Caolán McNamara <caolan.mcnamara@collabora.com>
Change-Id: Ic6cc3d51d4409bce6cc95137626debcab67dbc53
Reviewed-on: https://gerrit.collaboraoffice.com/c/online/+/10183
Tested-by: Jenkins CPCI <releng@collaboraoffice.com>
Reviewed-by: Noel Grandin <noel.grandin@collabora.com>
(cherry picked from commit a287185f62eaa49f03ab0b3b2e5d956221ef9997)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/210291
Tested-by: Jenkins
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>

external/python3/ExternalProject_python3.mk

@@ -45,6 +45,7 @@ $(call gb_ExternalProject_get_state_target,python3,build) :
 			/p:opensslIncludeDir=$(gb_UnpackedTarball_workdir)/openssl/include \
 			/p:opensslOutDir=$(gb_UnpackedTarball_workdir)/openssl \
 			/p:zlibDir=$(gb_UnpackedTarball_workdir)/zlib \
+			/p:KillPython=false \
 			/p:sqlite3Dir=$(gb_UnpackedTarball_workdir)/sqlite3 \
 			/p:lzmaDir=$(gb_UnpackedTarball_workdir)/lzma/ \
 			/p:mpdecimalDir=$(gb_UnpackedTarball_workdir)/python3/Modules/_decimal/ \