Update crosstool-ng 1.18.0 - Remove Caveats

To avoid the following error I decided to remove the caveats to avoid confusion:
```
[INFO ]  Installing libelf for host
[EXTRA]    Configuring libelf
[ERROR]    configure: error: no declaration for Elf32_Dyn
[ERROR]   
[ERROR]  >>
[ERROR]  >>  Build failed in step 'Installing libelf for host'
[ERROR]  >>        called in step '(top-level)'
[ERROR]  >>
[ERROR]  >>  Error happened in: CT_DoExecLog[scripts/functions@216]
[ERROR]  >>        called from: do_libelf_backend[scripts/build/companion_libs/200-libelf.sh@118]
[ERROR]  >>        called from: do_libelf_for_host[scripts/build/companion_libs/200-libelf.sh@60]
[ERROR]  >>        called from: do_companion_libs_for_host[scripts/build/companion_libs.sh@36]
[ERROR]  >>        called from: main[scripts/crosstool-NG.sh@632]
[ERROR]  >>
[ERROR]  >>  For more info on this error, look at the file: 'build.log'
[ERROR]  >>  There is a list of known issues, some with workarounds, in:
[ERROR]  >>      '/usr/local/Cellar/crosstool-ng/1.18.0/share/doc/crosstool-ng/ct-ng.1.18.0/B - Known issues.txt'
[ERROR]   
[ERROR]  (elapsed: 10:28.00)
[10:28] / make: *** [build] Error 1
```