window build doesn't apply PG_CPPFLAGS correctly

Hi

I tried to write test for plpgsql debug API, where I need to access to
plpgsql.h

I have line

PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpgsql/src

that is working well on unix, but it do nothing on windows

[00:05:14] Project "C:\projects\postgresql\pgsql.sln" (1) is building
"C:\projects\postgresql\test_dbgapi.vcxproj" (87) on node 1 (default
targets).
[00:05:14] PrepareForBuild:
[00:05:14] Creating directory ".\Release\test_dbgapi\".
[00:05:14] Creating directory ".\Release\test_dbgapi\test_dbgapi.tlog\".
[00:05:14] InitializeBuildStatus:
[00:05:14] Creating
".\Release\test_dbgapi\test_dbgapi.tlog\unsuccessfulbuild" because
"AlwaysCreate" was specified.
[00:05:14] ClCompile:
[00:05:14] C:\Program Files (x86)\Microsoft Visual Studio
12.0\VC\bin\x86_amd64\CL.exe /c /Isrc/include /Isrc/include/port/win32
/Isrc/include/port/win32_msvc /Zi /nologo /W3 /WX- /Ox /D WIN32 /D _WINDOWS
/D __WINDOWS__ /D __WIN32__ /D WIN32_STACK_RLIMIT=4194304 /D
_CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _WINDLL /D _MBCS
/GF /Gm- /EHsc /MD /GS /fp:precise /Zc:wchar_t /Zc:forScope
/Fo".\Release\test_dbgapi\\" /Fd".\Release\test_dbgapi\vc120.pdb" /Gd /TC
/wd4018 /wd4244 /wd4273 /wd4102 /wd4090 /wd4267 /errorReport:queue /MP
src/test/modules/test_dbgapi/test_dbgapi.c
[00:05:14] test_dbgapi.c
[00:05:16] src/test/modules/test_dbgapi/test_dbgapi.c(17): fatal error
C1083: Cannot open include file: 'plpgsql.h': No such file or directory
[C:\projects\postgresql\test_dbgapi.vcxproj]
[00:05:16] Done Building Project
"C:\projects\postgresql\test_dbgapi.vcxproj" (default targets) -- FAILED.
[00:05:16] Project "C:\projects\postgresql\pgsql.sln" (1) is building
"C:\projects\postgresql\test_ddl_deparse.vcxproj" (88) on node 1 (default
targets).

looks so PG_CPPFLAGS is not propagated to CPPFLAGS there.

Regards

Pavel