New issue by pullmoll on void-packages repository

https://github.com/void-linux/void-packages/issues/24020

Description:
Trying to build `mesa` for our `mips*` targets, which are `musl` only, results in an error about missing `libm-2.30.so`.
This happens only if the build environment is `i686`.
Using an `i686-musl` or `x86_64` build environment works fine, where the latter has differing word size which may cause other problems.

It seems that a host dependency makes its way into the target dependencies.

Here's the relevant output if that helps.
```
…
WARNING: Library target 'OSMesa' has 'name_prefix' set. Compilers may not find it from its '-lOSMesa' linker flag in the 'osmesa.pc' pkg-config file.
WARNING: Library target 'OSMesa' has 'name_prefix' set. Compilers may not find it from its '-lOSMesa' linker flag in the 'osmesa-uninstalled.pc' pkg-config file.
Message: Configuration summary:
        
        prefix:          /usr
        libdir:          lib
        includedir:      include
        
        OpenGL:          yes (ES1: yes ES2: yes)
        
        OSMesa:          libOSMesa(Gallium)
        
        DRI platform:    drm
        DRI drivers:     no
        DRI driver dir:  /usr/lib/dri
        
        GLX:             DRI-based
        
        EGL:             yes
        EGL drivers:     builtin:egl_dri2 builtin:egl_dri3
        GBM:             yes
        EGL/Vulkan/VL platforms:   x11 drm wayland surfaceless
        
        Vulkan drivers:  no
        
        llvm:            yes
        llvm-version:    10.0.0
        
        Gallium drivers: swrast
        Gallium st:      mesa
        HUD lmsensors:   yes
        
        Shared-glapi:    yes

Build targets in project: 113
WARNING: Project specifies a minimum meson_version '>= 0.46' but uses features which were added in newer versions:
 * 0.51.0: {'dep.get_variable'}
 * 0.52.0: {'version arg in find_program'}

Option buildtype is: plain [default: debugoptimized]
Option b_ndebug is: true [default: if-release]
Option cpp_std is: gnu++14 [default: c++14]
Found ninja-1.10.0 at /usr/bin/ninja
WARNING: custom_target 'glcpp-parse.[ch]' has more than one output! Using the first one.
WARNING: custom_target 'glsl_parser' has more than one output! Using the first one.
WARNING: custom_target 'program_parse_tab.[ch]' has more than one output! Using the first one.
=> mesa-20.1.4_2: running post_configure ...
=> mesa-20.1.4_2: running pre-build hook: 02-script-wrapper ...
=> mesa-20.1.4_2: running do_build ...
ninja: Entering directory `build'
ninja: error: '/usr/mips-linux-musl/usr/lib/libm-2.30.so', needed by 'src/gallium/targets/dri/libgallium_dri.so', missing and no known rule to make it
=> ERROR: mesa-20.1.4_2: do_build: '${make_cmd} -C ${meson_builddir} ${makejobs} ${make_build_args} ${make_build_target}' exited with 1
=> ERROR:   in do_build() at common/build-style/meson.sh:122
```

This would be a problem for people trying to cross build mips on their own.
Myself I can work around it as I have `i686-musl` also.