darwin.make-bootstrap-tools.test: fix build breakage

In the extremely unlikely case that our store hash path ends in several
digits (as is the case right now), the Darwin ld will try to interpret
those digits as a version number and barf. To avoid that, we pass in the
SDK version explicitly to stop it from trying to figure it out from iffy
context.

pkgs/stdenv/darwin/make-bootstrap-tools.nix

···
       export flags="-idirafter ${unpack}/include-Libsystem --sysroot=${unpack} -L${unpack}/lib"
 
       export CPP="clang -E $flags"
-      export CC="clang $flags -Wl,-rpath,${unpack}/lib -Wl,-v"
-      export CXX="clang++ $flags --stdlib=libc++ -lc++abi -isystem${unpack}/include/c++/v1 -Wl,-rpath,${unpack}/lib -Wl,-v"
+      export CC="clang $flags -Wl,-rpath,${unpack}/lib -Wl,-v -Wl,-sdk_version,10.10"
+      export CXX="clang++ $flags --stdlib=libc++ -lc++abi -isystem${unpack}/include/c++/v1 -Wl,-rpath,${unpack}/lib -Wl,-v -Wl,-sdk_version,10.10"
 
       echo '#include <stdio.h>' >> foo.c
       echo '#include <float.h>' >> foo.c