termscp: fix darwin build

I was running into Foundation.h errors during compilation on mac/darwin,
adding Foundation fixes that for me.

Error:

```
The following warnings were emitted during compilation:

warning: In file included from objc/notify.m:1:
warning: objc/notify.h:1:9: fatal error: 'Foundation/Foundation.h' file not found
warning: #import <Foundation/Foundation.h>
warning:         ^~~~~~~~~~~~~~~~~~~~~~~~~
warning: 1 error generated.

error: failed to run custom build command for `mac-notification-sys v0.3.0`

Caused by:
  process didn't exit successfully: `/tmp/cargo-installEt3UWW/release/build/mac-notification-sys-f414f8995c05e541/build-script-build` (exit status: 1)
  --- stdout
  TARGET = Some("x86_64-apple-darwin")
  OPT_LEVEL = Some("3")
  HOST = Some("x86_64-apple-darwin")
  CC_x86_64-apple-darwin = None
  CC_x86_64_apple_darwin = None
  HOST_CC = None
  CC = Some("clang")
  CFLAGS_x86_64-apple-darwin = None
  CFLAGS_x86_64_apple_darwin = None
  HOST_CFLAGS = None
  CFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("false")
  running: "clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "--target=x86_64-apple-darwin" "-fmodules" "-o" "/tmp/cargo-installEt3UWW/release/build/mac-notification-sys-ce5dd87fdfef4721/out/objc/notify.o" "-c" "objc/notify.m"
  cargo:warning=In file included from objc/notify.m:1:
  cargo:warning=objc/notify.h:1:9: fatal error: 'Foundation/Foundation.h' file not found
  cargo:warning=#import <Foundation/Foundation.h>
  cargo:warning=        ^~~~~~~~~~~~~~~~~~~~~~~~~
  cargo:warning=1 error generated.
  exit status: 1

  --- stderr

  error occurred: Command "clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "--target=x86_64-apple-darwin" "-fmodules" "-o" "/tmp/cargo-installEt3UWW/release/build/mac-notification-sys-ce5dd87fdfef4721/out/objc/notify.o" "-c" "objc/notify.m" with args "clang" did not execute successfully (status code exit status: 1).

warning: build failed, waiting for other jobs to finish...
error: failed to compile `termscp v0.7.0`, intermediate artifacts can be found at `/tmp/cargo-installEt3UWW`

Caused by:
  build failed
```

1 files changed, 2 insertions, 0 deletions

diff --git a/pkgs/tools/networking/termscp/default.nix b/pkgs/tools/networking/termscp/default.nix
index 3bc12747b74..58bbfe5e46c 100644
--- a/pkgs/tools/networking/termscp/default.nix
+++ b/pkgs/tools/networking/termscp/default.nix
@@ -5,6 +5,7 @@
 , openssl
 , pkg-config
 , rustPlatform
+, Foundation
 , Security
 , stdenv
 }:
@@ -31,6 +32,7 @@ rustPlatform.buildRustPackage rec {
     libssh
     openssl
   ] ++ lib.optional stdenv.isDarwin [
+    Foundation
     Security
   ];