{bintools,cc}-wrapper: fix static builds on Darwin

Without this change, all Darwin platforms mangle to the same suffix
salt. That is normally not an issue because build = host should mean a
non-cross build, but it causes issues on Darwin with static builds
because `DEVELOPER_DIR_FOR_BUILD` and `DEVELOPER_DIR` will refer to
different SDKs but mangle to the same `DEVELOPER_DIR` with suffix salt.

The fix is to mangle static builds differently from non-static ones on
Darwin, which allows building for a static Darwin target on a
same-architecture Darwin host. This fix is applied only to Dariwn
because the issue does not appear to affect other platforms.

pkgs/build-support/bintools-wrapper/default.nix

···
   coreutils_bin = optionalString (!nativeTools) (getBin coreutils);
 
   # See description in cc-wrapper.
-  suffixSalt = replaceStrings ["-" "."] ["_" "_"] targetPlatform.config;
+  suffixSalt = replaceStrings ["-" "."] ["_" "_"] targetPlatform.config
+    + lib.optionalString (targetPlatform.isDarwin && targetPlatform.isStatic) "_static";
 
   # The dynamic linker has different names on different platforms. This is a
   # shell glob that ought to match it.

pkgs/build-support/cc-wrapper/default.nix

···
   # without interfering. For the moment, it is defined as the target triple,
   # adjusted to be a valid bash identifier. This should be considered an
   # unstable implementation detail, however.
-  suffixSalt = replaceStrings ["-" "."] ["_" "_"] targetPlatform.config;
+  suffixSalt = replaceStrings ["-" "."] ["_" "_"] targetPlatform.config
+    + lib.optionalString (targetPlatform.isDarwin && targetPlatform.isStatic) "_static";
 
   useGccForLibs = useCcForLibs
     && libcxx == null