[ISSUE] cmake build style doesn't allow to choose source dir

[yopito <yopito@users.noreply.github.com>]

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New issue by yopito on void-packages repository

https://github.com/void-linux/void-packages/issues/20878

Description:
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### System

* xuname:  Void 5.4.31_1 x86_64-musl GenuineIntel uptodate rrnFF

* package:  packaging shiboken2 update to 5.14.2 (WIP)


### Expected behavior

want to use cmake with sources of a subdir of $wkrsrc via `-S` cmake flag:
```
[...]
wrksrc="${_pkgname}"
build_style=cmake
configure_args=" ... -S sources/shiboken2"
[...]
```
### Actual behavior

`-S <subdir>` has no effect.

### Additional details

xbps-src append "`../`" to cmake arguments unconditionally.  
Resulting command is something like `cmake (args) -S sources/shiboken2 ../`

So cmake uses sources of ${wrksrc}/build/.. instead of ${wrksrc}/sources/shiboken2/

Implied by `common/build-style/cmake.sh` on sed expression L63:

```
    60          # Override flags: https://gitlab.kitware.com/cmake/cmake/issues/19590
    61          CFLAGS="${CFLAGS/ -pipe / }" CXXFLAGS="${CXXFLAGS/ -pipe / }" \
    62                  cmake ${cmake_args} ${configure_args} $(echo ${cmake_builddir}|sed \
    63                          -e 's|[^/]$|/|' -e 's|[^/]*||g' -e 's|/|../|g')
    64
```
### Workaround

My current workaround: adding subdir to $wrksrc:

```
wrksrc="${_pkgname}/sources/shiboken2"
build_style=cmake
configure_args=" ... "  # removed " -S sources/shiboken2 "
[...]
```
... that makes xlint nervous:
```
srcpkgs/shiboken2/template:7: wrksrc should be a top-level directory
```