[clang] [CMake] Enable static libxml2 for Fuchsia toolchain (PR #191657)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-sparc64-linux` running on `debian-stadler-sparc64` while building `clang` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/114/builds/406

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: Tooling/clang-diff-ast.cpp' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
/var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/bin/clang-diff -ast-dump /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/clang/test/Tooling/clang-diff-ast.cpp -- -std=c++11 | /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/bin/FileCheck /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/clang/test/Tooling/clang-diff-ast.cpp
# executed command: /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/bin/clang-diff -ast-dump /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/clang/test/Tooling/clang-diff-ast.cpp -- -std=c++11
# note: command had no output on stdout or stderr
# error: command failed with exit status: -4
# executed command: /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/bin/FileCheck /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/clang/test/Tooling/clang-diff-ast.cpp
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/stage1/bin/FileCheck /var/lib/buildbot/workers/debian-stadler-sparc64/clang-sparc64-linux/llvm/clang/test/Tooling/clang-diff-ast.cpp
# `-----------------------------
# error: command failed with exit status: 2

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/191657