BUG: Removed too much from the MSVC workaround

[tuxillo]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

Building math/py-pandas in DragonFly BSD results in:

building 'pandas._libs.window.aggregations' extension                                                                                  
cc -Wno-unused-result -Wsign-compare -DNDEBUG -pipe -I/usr/local/include -I/usr/local/include/ncurses -O2 -fno-strict-aliasing -pipe -O
2 -fno-strict-aliasing -fPIC -DNPY_NO_DEPRECATED_API=0 -Ipandas/_libs/window -I/usr/local/lib/python3.9/site-packages/numpy/core/includ
e -I/usr/local/include/python3.9 -c pandas/_libs/window/aggregations.cpp -o build/temp.dragonfly-6.5-DEVELOPMENT-x86_64-cpython-39/pand
as/_libs/window/aggregations.o                                                                                                         pandas/_libs/window/aggregations.cpp: In function 'void __pyx_f_6pandas_5_libs_6window_12aggregations_add_mean(__pyx_t_5numpy_float64_t
, Py_ssize_t*, __pyx_t_5numpy_float64_t*, Py_ssize_t*, __pyx_t_5numpy_float64_t*, __pyx_t_5numpy_int64_t*, __pyx_t_5numpy_float64_t*)':
pandas/_libs/window/aggregations.cpp:4784:18: error: 'signbit' was not declared in this scope                                          
     __pyx_t_1 = (signbit(__pyx_v_val) != 0);                                                                                          
                  ^~~~~~~                                                                                                              
pandas/_libs/window/aggregations.cpp:4784:18: note: suggested alternative:                                                             
In file included from /usr/include/c++/8.0/complex:44,                                                                                 
                 from pandas/_libs/window/aggregations.cpp:1028:                                                                       
/usr/include/c++/8.0/cmath:677:5: note:   'std::signbit'                                                                               
     signbit(_Tp __x)                                                                                                                  
     ^~~~~~~                                                                                                                           
pandas/_libs/window/aggregations.cpp: In function 'void __pyx_f_6pandas_5_libs_6window_12aggregations_remove_mean(__pyx_t_5numpy_float6
4_t, Py_ssize_t*, __pyx_t_5numpy_float64_t*, Py_ssize_t*, __pyx_t_5numpy_float64_t*)':                                                 
pandas/_libs/window/aggregations.cpp:4951:18: error: 'signbit' was not declared in this scope                                          
     __pyx_t_1 = (signbit(__pyx_v_val) != 0);                                                                                          
                  ^~~~~~~                                                                                                              
pandas/_libs/window/aggregations.cpp:4951:18: note: suggested alternative:                                                             
In file included from /usr/include/c++/8.0/complex:44,                                                                                 
                 from pandas/_libs/window/aggregations.cpp:1028:                                                                       
/usr/include/c++/8.0/cmath:677:5: note:   'std::signbit'                                                                               
     signbit(_Tp __x)                                                                                                                  
     ^~~~~~~                                                                                                                           
error: command '/usr/bin/cc' failed with exit code 1                                                                                   
*** Error code 1

Issue Description

When removing the MSVC workaround here (#45008), too much code was removed and the #else case where cmath was included plus the cdef extern declaration in aggregations.pyx should have been kept for the systems that can't provide cmath C++ functions from cmath.h (or at least that's my understanding).

I also think that the MVS macro conditional down below was for z/OS (belonging to #35829) and not for MSVC so this potentially also broke the build there, althought I have not tested it myself:

++#elif defined(__MVS__)
++#include <cmath>
++

Expected Behavior

The build to be successful :)

Installed Versions

pandas.show_versions()

INSTALLED VERSIONS

commit : 91111fd
python : 3.9.16.final.0
python-bits : 64
OS : DragonFly
OS-release : 6.5-DEVELOPMENT
Version : DragonFly v6.5.0.1.gb1258-DEVEL
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : None
LOCALE : None.None

pandas : 1.5.1
numpy : 1.23.5
pytz : 2022.7
dateutil : 2.8.2
setuptools : 63.1.0
pip : None
Cython : 0.29.32
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : 1.3.5
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : None
numba : None
numexpr : 2.8.4
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : None
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None
tzdata : None

[tuxillo]

Any news? :)