Restrict HelloWorldRust because we have a fair bit of breakage

H/HelloWorldRust/build_tarballs.jl

@@ -13,10 +13,19 @@ mkdir -p ${prefix}/bin
 rustc -o ${prefix}/bin/hello_world${exeext} -g /usr/share/testsuite/rust/hello_world/hello_world.rs
 """
 
-# These are the platforms we will build for by default, unless further
-# platforms are passed in on the command line
+# We build for a restricted set of platforms, because our rust toolchain is a little broken
 platforms = supported_platforms()
 
+# First, FreeBSD has -fPIC problems when linking in `crt.o`
+filter!(p -> !isa(p, FreeBSD), platforms)
+
+# Next, :musl libcs have a hard time linking
+filter!(p -> libc(p) != :musl, platforms)
+
+# Finally, windows seems to be broken
+# https://github.com/JuliaPackaging/BinaryBuilder.jl/issues/499
+filter!(p -> !isa(p, Windows), platforms)
+
 # The products that we will ensure are always built
 products = [
     ExecutableProduct("hello_world", :hello_world),