There's a closed pull request on the void-packages repository

llvm11: update to 11.1.0.
https://github.com/void-linux/void-packages/pull/29431

Description:
Also:
- Clean up template.
- Update `srcpkgs/llvm11/update` due to #29429.

Fixes: #28609.
Fixes: #17935.

<!-- Mark items with [x] where applicable -->

#### General
- [ ] This is a new package and it conforms to the [quality requirements](https://github.com/void-linux/void-packages/blob/master/Manual.md#quality-requirements)

#### Have the results of the proposed changes been tested?
- [x] I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
- [ ] I generally don't use the affected packages but briefly tested this PR

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#### Does it build and run successfully? 
- [x] I built this PR locally for my native architecture, x86_64-musl
- [x] I built this PR locally for these architectures (TODO):
  - [x] aarch64-musl
  - [ ] armv7l
  - [ ] armv6l-musl
  - [ ] ppc-musl
  - [ ] ppc
  - [ ] ppcle-musl
  - [ ] ppcle
  - [ ] ppc64-musl
  - [ ] ppc64
  - [ ] ppc64le-musl
  - [ ] ppc64le

Currently, the documentation fails to build:
```
[2824/5792] Generating man Sphinx documentation for clang-tools into "/builddir/llvm-project-11.1.0.src/llvm/build/tools/clang/tools/extra/docs/man"
FAILED: tools/clang/tools/extra/docs/CMakeFiles/docs-clang-tools-man 
cd /builddir/llvm-project-11.1.0.src/llvm/build/tools/clang/tools/extra/docs && /usr/bin/sphinx-build -b man -d /builddir/llvm-project-11.1.0.src/llvm/build/tools/clang/tools/extra/docs/_doctrees-clang-tools-man -q -t builder-man -W /builddir/llvm-project-11.1.0.src/clang-tools-extra/docs /builddir/llvm-project-11.1.0.src/llvm/build/tools/clang/tools/extra/docs/man

Warning, treated as error:
/builddir/llvm-project-11.1.0.src/clang-tools-extra/docs/clang-tidy/Integrations.rst::"table cell spanning" not supported
```

### List of packages to rebuild:
H = hostmakedepends, M = makedepends, C = checkdepends:
- [ ] 0ad: H=*clang*
- [ ] afl: H=*clang*,*llvm*
- [ ] ardour: H=*clang*
- [ ] bat: H=*clang*,*llvm*
- [ ] bcc: M=*clang*,*clang-tools-extra*,*lld-devel*,*llvm*
- [ ] beignet: H=*clang*,*llvm*
- [ ] blender: M=*llvm*
- [ ] bpftrace: M=*clang*,*clang-tools-extra*,*llvm*
- [ ] ccls: H=*clang-tools-extra* M=*clang-tools-extra*,*llvm*
- [ ] chromium: H=*clang*
- [ ] clazy: M=*clang*,*llvm* D=*clang*
- [ ] codelite: H=*clang* M=*lldb-devel*
- [ ] deadbeef: H=*clang*
- [ ] discord-ptb: D=*libcxx*
- [ ] discord: D=*libcxx*
- [ ] electron10: H=*clang*
- [ ] electron9: H=*clang*
- [ ] faust: H=*llvm* M=*llvm-libunwind-devel*
- [ ] firefox-esr: H=*llvm*,*clang*
- [ ] firefox: H=*llvm*,*clang*
- [ ] ghdl: M=*llvm11*
- [ ] gnome-builder: H=*llvm* M=*clang*
- [ ] godot: H=*clang*
- [ ] hedgewars: H=*clang*
- [ ] hfsprogs: H=*clang*
- [ ] include-what-you-use: M=*clang*,*clang-tools-extra*,*llvm*
- [ ] ispc: H=*clang*,*clang-tools-extra*,*llvm*
- [ ] juCi++: M=*clang*
- [ ] kdevelop: H=*llvm* M=*clang*
- [ ] ldc: H=*llvm11*
- [ ] mesa: H=*llvm* clang M=*clang*,*libclc* D=*libclc*
- [ ] meson: C=*clang*,*llvm*
- [ ] mozjs78: H=*llvm*,*clang*
- [ ] multitail: H=*clang-analyzer*
- [ ] pijul: H=*clang*
- [ ] qt5-doc: H=*clang*
- [ ] qt5: H=*clang*
- [ ] qtcreator: H,M=*clang*,*llvm*
- [ ] qv4l2: H=*clang*
- [ ] rdedup: H=*clang*
- [ ] rtags: H=*clang* M=*llvm*
- [ ] rust: H=*llvm11* M=*llvm11*
- [ ] shiboken2: M=*clang* D=*clang*
- [ ] thunderbird: H=*llvm*,*clang*
- [ ] zig: M=*clang*,*llvm11*,*lld-devel*

[ci skip]