rust: link against zlib and ncurses explicitly

else, librustc_codegen_llvm-llvm.so doesn't get linked against them
when cross compiling

fixes https://github.com/void-linux/void-packages/issues/4379

[ci skip]

srcpkgs/rust/patches/llvm-with-dependencies.patch

@@ -0,0 +1,13 @@
+--- rustc-1.30.0-src/src/librustc_llvm/lib.rs.orig
++++ rustc-1.30.0-src/src/librustc_llvm/lib.rs
+@@ -121,3 +121,10 @@
+                  LLVMInitializeWebAssemblyTargetMC,
+                  LLVMInitializeWebAssemblyAsmPrinter);
+ }
++
++#[link(name = "ffi")]
++extern {}
++#[link(name = "z")]
++extern {}
++#[link(name = "ncursesw")]
++extern {}

srcpkgs/rust/patches/llvm-with-ffi.patch

@@ -1,9 +0,0 @@
---- rustc-1.21.0-src/src/librustc_llvm/lib.rs.orig
-+++ rustc-1.21.0-src/src/librustc_llvm/lib.rs
-@@ -425,3 +425,6 @@
-         }
-     }
- }
-+
-+#[link(name = "ffi")]
-+extern {}