bootstrap: Don't force -static for musl targets in cc-rs

I can't really make sense of this part. For musl targets that default to
static linkage, crt-static is set as a target feature and cc-rs should
be able to correctly infer that -static should be used. However, you
cannot compile rustc or run the tests with +crt-static, so you'd have to
disable it in bootstrap.toml anyways, bypassing this codepath entirely.
But for targets that are defaulting to dynamic linkage, hardcoding
-static for all musl targets in cc_detect just doesn't make sense. It
breaks the run-make tests because the compiler defaults (and is
configured!) to dynamically link dylibs, but the cc-rs configuration is
hardcoded to link them statically, which will fail.

Signed-off-by: Jens Reidel <adrian@travitia.xyz>

Author: Gelbpunkt

src/bootstrap/src/utils/cc_detect.rs

@@ -48,9 +48,6 @@ fn new_cc_build(build: &Build, target: TargetSelection) -> cc::Build {
             if target.is_msvc() {
                 cfg.static_crt(true);
             }
-            if target.contains("musl") {
-                cfg.static_flag(true);
-            }
         }
     }
     cfg