set llvm.assertions to false in compiler profile

Having this set to true disrupts compiler development workflows for people who use `llvm.download-ci-llvm = true`
because we don't provide ci-llvm on the `rustc-alt-builds` server. Therefore, it is kept off by default.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

src/bootstrap/defaults/config.compiler.toml

@@ -19,9 +19,9 @@ lto = "off"
 frame-pointers = true
 
 [llvm]
-# This enables debug-assertions in LLVM,
-# catching logic errors in codegen much earlier in the process.
-assertions = true
+# Having this set to true disrupts compiler development workflows for people who use `llvm.download-ci-llvm = true`
+# because we don't provide ci-llvm on the `rustc-alt-builds` server. Therefore, it is kept off by default.
+assertions = false
 # Enable warnings during the LLVM compilation (when LLVM is changed, causing a compilation)
 enable-warnings = true
 # Will download LLVM from CI if available on your platform.