Disable -Werror on aarch64-apple-darwin (#296)

* Disable `-Werror` on `aarch64-apple-darwin`

The new `clang` interacts badly with LLVM headers, giving the fatal
error message:

```
/Users/julia/.julia/scratchspaces/a66863c6-20e8-4ff4-8a62-49f30b1f605e/agent-cache/default-honeycrisp-P2C257CXGN.0/build/default-honeycrisp-P2C257CXGN-0/julialang/julia-master/usr/include/llvm/ADT/DenseMap.h:129:16: error: variable 'NumEntries' set but not used [-Werror,-Wunused-but-set-variable]
      unsigned NumEntries = getNumEntries();
               ^
```

Example: https://buildkite.com/julialang/julia-master/builds/23068#0187a57a-fa1f-45ca-8811-a0637827e3da/438-895

We would ideally like to just pass -Wno-unused-but-set-variable` but our makefile variable setting scripts are not sophisticated enough to allow spaces in these values. :(

Author: staticfloat

Makefile

@@ -9,3 +9,6 @@ sign_treehashes:
 
 verify_treehashes:
 	cd .buildkite/cryptic_repo_root && verify_treehashes --repo-root=$$(pwd) --verbose
+
+print-%:
+	echo "$*=$($*)"

pipelines/main/launch_signed_jobs.yml.signature

@@ -1 +1,3 @@
-Salted__墳��^$i?��:	���:��;�ޓ���e߫Lت��2�K>��&�𬸑���+U�0�^_�,��j�gD���g=���_v�
+Salted__��Ib
+k�Zn���np��0FiY8�'ݖ�|/��c�վ�R�}��8�i^I�
+]@z���i�[���i�bjc���U?	�}���x

pipelines/main/launch_upload_jobs.yml.signature

@@ -1,3 +1,3 @@
-Salted__2��;-.%��������9�~I��G�Z�
-����
%[��Pd���o�%�,��������S(�
-�<bD�gZ����N�c*f
+Salted__/���(�>�j���'׊��m�I4�* ��%�g^�
+����|W�_�����2:�[��F:�
+�F�����)n�'q`��4,�

pipelines/main/platforms/build_macos.arches

@@ -1,6 +1,6 @@
 # OS       TRIPLET                  ARCH          MAKE_FLAGS                                TIMEOUT
 macos      x86_64-apple-darwin      x86_64        JL_CFLAGS=-Werror,JL_CXXFLAGS=-Werror     .
-macos      aarch64-apple-darwin     aarch64       JL_CFLAGS=-Werror,JL_CXXFLAGS=-Werror     .
+macos      aarch64-apple-darwin     aarch64       .                                         .
 
 # These special lines allow us to embed default values for the columns above.
 # Any column without a default mapping here will simply substitute a `.` to the empty string

pipelines/scheduled/coverage/coverage.yml.signature

@@ -1 +1 @@
-Salted__�Y+FB��k�Z�u��lA,�{*�ے�캧e�a����Boh��R;g���@����P��F2�qaI0�&{�j��1�{��x@Y
+Salted__S�ø�[��X�ш(Z����+�%ˣB����N�$~*�P�9��?�:�-G�w2�J=�6��v��j�(�M �p�k3��S���oR�B

pipelines/scheduled/launch_signed_jobs.yml.signature

@@ -1,6 +1,6 @@
 # OS       TRIPLET                      ARCH          MAKE_FLAGS                                               TIMEOUT
 macos      x86_64-apple-darwinnogpl     x86_64        USE_GPL_LIBS=0,JL_CFLAGS=-Werror,JL_CXXFLAGS=-Werror     .
-macos      aarch64-apple-darwinnogpl    aarch64       USE_GPL_LIBS=0,JL_CFLAGS=-Werror,JL_CXXFLAGS=-Werror     .
+macos      aarch64-apple-darwinnogpl    aarch64       USE_GPL_LIBS=0                                           .
 
 # These special lines allow us to embed default values for the columns above.
 # Any column without a default mapping here will simply substitute a `.` to the empty string