fix(main/libllvm): enable RTTI

[robertkirkman]

• Necessary to fix this error that otherwise would occur when attempting to launch the software qt-creator:

qtc.extensionsystem.plugin: [ ClangFormat ] Plugin error:
/data/data/com.termux/files/usr/lib/qtcreator/plugins/libClangFormat.so:
Cannot load library /data/data/com.termux/files/usr/lib/qtcreator/plugins/libClangFormat.so:
dlopen failed: cannot locate symbol "_ZTIN4llvm3vfs10FileSystemE"
referenced by "/data/data/com.termux/files/usr/lib/qtcreator/plugins/libClangFormat.so"...

• All other major UNIX-like operating systems enable this. See addpkg(x11/qt-creator): 18.0.0 #27309 (comment)

[robertkirkman]

LLVM and Flang can only build in a PR by themselves within 6 hours, so it will be necessary to merge this first before any of the other packages that depend on it, then I will update the other PR to rebuild all reverse dependencies afterward.

[robertkirkman]

Unfortunately there is a cloudflare outage, so this cannot be built for now.

https://www.cloudflarestatus.com/

[robertkirkman]

The cloudflare and github outages are resolved. I will merge this in 24 hours if there are no objections to this.

If a test case where a noticeable performance difference in libllvm with -DLLVM_ENABLE_RTTI=ON is found, please mention it. If found, it might be important to benchmark that to evaluate the impact.

Even Alpine Linux, which has a reputation as a lightweight distro, has -DLLVM_ENABLE_RTTI=ON.

[finagolfin]

I looked around the web a bit and haven't seen indications that it will cause major slowdowns- people seem to be reporting small increases in compilation time in some scenarios- so let's try it and see.