Fix getdeps build failure on CentOS Stream 9

Summary:
The gcc14 manifest (added in D96393589) is RPM-only — it has no [git] or
[download] section. When cachelib lists it as a [dependencies] entry, getdeps
tries to create a fetcher for gcc14 during build. The fetcher checks if the
gcc-toolset-14 RPM is installed via `rpm -q`; if not, there is no fallback and
the build fails with:

  KeyError: 'project gcc14 has no fetcher configuration matching ...'

The install-system-deps command uses `--skip-broken`, so if gcc-toolset-14 is
not available in the user's repos it is silently skipped, leaving the build to
fail with a confusing error.

Fix: declare gcc-toolset-14 as a system package ([rpms]) on the cachelib
manifest itself instead of pulling it in via a separate gcc14 [dependencies]
entry. This way:
- install-system-deps still installs the RPM (it collects rpms from the project
  manifest).
- During build, cachelib uses its own [git] fetcher; gcc14 is no longer
  resolved as a separate project so no fetcher is needed for it.
- If gcc-toolset-14 is missing, cmake fails with a clear "compiler not found"
  error instead of a cryptic KeyError.

Reviewed By: rlyerly

Differential Revision: D99142094

fbshipit-source-id: 6496d4e515aa5495049f6e76e50dd6f982714b51

Author: pbhandar2

build/fbcode_builder/manifests/cachelib

@@ -30,8 +30,8 @@ magic_enum
 # specific configuration we rely on the folly manifest to provide this
 # dependency to avoid duplication.
 
-[dependencies.all(distro=centos_stream,distro_vers=9)]
-gcc14
+[rpms.all(distro=centos_stream,distro_vers=9)]
+gcc-toolset-14
 
 [cmake.defines.all(distro=centos_stream,distro_vers=9)]
 CMAKE_C_COMPILER=/opt/rh/gcc-toolset-14/root/usr/bin/gcc