[ISSUE] Boost & aarch64

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

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New issue by unspecd on void-packages repository

https://github.com/void-linux/void-packages/issues/27398

Description:
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### System

* xuname:  
  *Void 5.10.2_1 x86_64-musl GenuineIntel uptodate rrrnFFFFFFFFF*
* package:  
  *boost-1.72.0_4*

I'm trying to build `gnucash` for `aarch64-musl`:

```sh
[ 96%] Linking CXX executable ../bin/gnucash
/usr/lib/gcc/aarch64-linux-musl/9.3.0/../../../../aarch64-linux-musl/bin/ld: ../lib/gnucash/libgnc-csv-import.so: undefined reference to `boost::icu_regex_traits::isctype(int, unsigned long) const'
/usr/lib/gcc/aarch64-linux-musl/9.3.0/../../../../aarch64-linux-musl/bin/ld: ../lib/gnucash/libgnc-csv-import.so: undefined reference to `boost::re_detail_107200::icu_regex_traits_implementation::do_transform(int const*, int const*, icu_67::Collator const*) const'
/usr/lib/gcc/aarch64-linux-musl/9.3.0/../../../../aarch64-linux-musl/bin/ld: ../lib/gnucash/libgnc-csv-import.so: undefined reference to `boost::basic_regex<int, boost::icu_regex_traits>::do_assign(int const*, int const*, unsigned int)'
```

### Steps to reproduce the behavior
```sh
$ echo 'make_build_args="VERBOSE=1 gnucash"' >> srcpkgs/gnucash/template
$ ./xbps-src -a aarch64-musl build gnucash
```