Closed issue by Johnnynator on void-packages repository

https://github.com/void-linux/void-packages/issues/11740
Description: ### System

* xuname:  
  *output of ``xuname`` (part of xtools)*
* package:  
  *affected package(s) including the version*

show-build-deps does not strip trailing `-` version separator when using `-E` for hostmakedepends that exist in local repo, this might also be an issue for makedepends but I haven't tested anything else, just sharing my observations. 

### Expected behavior
```
./xbps-src -m masterdir-musl -a armv7l show-build-deps mailimporter
cmake
extra-cmake-modules
kcoreaddons
libkdepim
python
qt5
```
### Actual behavior
```
./xbps-src -E -m masterdir-musl -a armv7l show-build-deps mailimporter
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
/media/SourceCode/void-packages/common/xbps-src/shutils/build_dependencies.sh: line 169: unset: XBPS_BINPKG_EXISTS: cannot unset: readonly variable
cmake
extra-cmake-modules-
kcoreaddons-
libkdepim
python
qt5
```
### Steps to reproduce the behavior
TODO: explain a simple case to reproduce it :)