Rollup merge of #106464 - djkoloski:update_fuchsia_platform_support_docs, r=tmandry

Update Fuchsia walkthrough with new configs

The new `download-ci-llvm` configuration option dosn't work with `lld = true` (see #100853). The Fuchsia walkthrough should recommend setting it to `false`.

r? `@tmandry`

Author: compiler-errors

src/doc/rustc/src/platform-support/fuchsia.md

@@ -198,6 +198,9 @@ target = ["<host_platform>", "aarch64-fuchsia", "x86_64-fuchsia"]
 [rust]
 lld = true
 
+[llvm]
+download-ci-llvm = false
+
 [target.x86_64-fuchsia]
 cc = "clang"
 cxx = "clang++"