macOS 10.14 runners are no longer available via Azure Pipeline

These images have already been deprecated for two months[1].  Thus,
we upgrade to macOS 10.15.  Since clang 12 is picky about
`int-in-bool-context` warning, we disable `-Werror`.

[1] <https://devblogs.microsoft.com/devops/hosted-pipelines-image-deprecation/>

azure/macos/job.yml

@@ -5,7 +5,7 @@ parameters:
 jobs:
   - job: ${{ parameters.configurationName }}
     pool:
-      vmImage: 'macOS-10.14'
+      vmImage: 'macOS-10.15'
     steps:
     - template: brew.yml
     - script: |
@@ -66,7 +66,6 @@ jobs:
             --enable-intl \
             --with-mhash \
             --with-sodium \
-            --enable-werror \
             --with-config-file-path=/etc \
             --with-config-file-scan-dir=/etc/php.d
       displayName: 'Configure Build'