gistfile1.txt

        cl -I./include -I./include/pmc -nologo -GF -W4 -MD -Zi -DNDEBUG -Ox -GL
-fp:precise -DWIN32 -D_CONSOLE -DNO_STRICT -DWIN64 -DCONSERVATIVE -DUSE_SITECUST
OMIZE  -D_CRT_SECURE_NO_DEPRECATE -DHASATTRIBUTE_DEPRECATED -wd4101 -DHASATTRIBU
TE_NORETURN -wd4101 -Zi     -wd4127 -wd4054 -wd4310 -Isrc/dynpmc -Isrc/ -Fosrc/d
ynpmc/os.obj -c src/dynpmc/os.c
os.c
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(19) : warning C4431: missing typ
e specifier - int assumed. Note: C no longer supports default-int
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(19) : error C2054: expected '('
to follow 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(19) : error C2085: 'Parrot_OS_ge
t_vtable_pointer' : not in formal parameter list
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(20) : error C2061: syntax error
: identifier 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(21) : warning C4431: missing typ
e specifier - int assumed. Note: C no longer supports default-int
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(21) : error C2054: expected '('
to follow 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(21) : error C2085: 'Parrot_OS_up
date_vtable' : not in formal parameter list
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(22) : error C2061: syntax error
: identifier 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(23) : warning C4431: missing typ
e specifier - int assumed. Note: C no longer supports default-int
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(23) : error C2054: expected '('
to follow 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(23) : error C2085: 'Parrot_OS_ge
t_vtable' : not in formal parameter list
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(24) : error C2061: syntax error
: identifier 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(25) : warning C4431: missing typ
e specifier - int assumed. Note: C no longer supports default-int
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(25) : error C2054: expected '('
to follow 'PARROT_DYNEXT_EXPORT'
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(25) : error C2085: 'Parrot_OS_ge
t_mro' : not in formal parameter list
c:\consulting\rakudo\parrot\src\dynpmc\pmc_os.h(26) : error C2061: syntax error
: identifier 'PARROT_DYNEXT_EXPORT'
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 10.0
\VC\BIN\amd64\cl.EXE"' : return code '0x2'
Stop.

Thanks! As it turns out, the pmclass os was a static pmc, not a dynpmc. So windows reveiled duplicate symbols, the wrong EXPORT attribute and more issues.
Fixed in latest parrot master.