bazel: Fix build on darwin

* use default stdenv (clang 7)
* add no-arc.patch to make the xcode_locate tool compile without libarc-lite
* remove the `-mmacosx-version-min=10.9` flag from the bootstrap compile script

pkgs/development/tools/build-managers/bazel/bazel_3/default.nix

@@ -176,6 +176,14 @@ stdenv.mkDerivation rec {
     # argument if it's found to be an empty string.
     ../trim-last-argument-to-gcc-if-empty.patch
 
+    # On Darwin, using clang 6 to build fails because of a linker error (see #105573),
+    # but using clang 7 fails because libarclite_macosx.a cannot be found when linking
+    # the xcode_locator tool.
+    # This patch removes using the -fobjc-arc compiler option and makes the code
+    # compile without automatic reference counting. Caveat: this leaks memory, but
+    # we neglect this fact.
+    ./no-arc.patch
+
     # --experimental_strict_action_env (which may one day become the default
     # see bazelbuild/bazel#2574) hardcodes the default
     # action environment to a non hermetic value (e.g. "/usr/local/bin").
@@ -371,6 +379,8 @@ stdenv.mkDerivation rec {
         src/tools/xcode/stdredirect/BUILD \
         tools/osx/BUILD
 
+      substituteInPlace scripts/bootstrap/compile.sh --replace ' -mmacosx-version-min=10.9' ""
+
       # nixpkgs's libSystem cannot use pthread headers directly, must import GCD headers instead
       sed -i -e "/#include <pthread\/spawn.h>/i #include <dispatch/dispatch.h>" src/main/cpp/blaze_util_darwin.cc