Manually build re2c on macos

Avoid issues with the licensing mafia, see:
Homebrew/homebrew-core#59094

Closes GH-5932.

Author: nikic

azure/macos/brew.yml

@@ -7,8 +7,7 @@ steps:
   - script: |
       brew install pkg-config \
                    autoconf \
-                   bison \
-                   re2c
+                   bison
     displayName: 'Install Build Tools'
   - script: |
       brew install openssl@1.1 \
@@ -34,3 +33,11 @@ steps:
       brew upgrade libzip
       brew link icu4c gettext --force
     displayName: 'Install Build Dependencies'
+  - script: |
+      wget https://github.com/skvadrik/re2c/releases/download/2.0.1/re2c-2.0.1.tar.xz
+      tar -xf re2c-2.0.1.tar.xz
+      cd re2c-2.0.1
+      ./configure
+      make -j$(sysctl -n hw.ncpu)
+      make install
+    displayName: 'Build re2c'