Fix compilation on macOS (#68)

* Make macOS CI script pick the right Clang version

* Fix 'implicit instantiation of undefined template' error

Here is the error:

```
/Users/anton/zilliqa/scilla-rtl/testsuite/ContrTests.cpp:147:23: error: implicit instantiation of undefined template 'std::basic_ofstream<char>'
        std::ofstream Out(PathPrefix + Input.ExpectedStateFilename);
                      ^
/usr/local/opt/llvm@13/bin/../include/c++/v1/iosfwd:149:32: note: template is declared here
    class _LIBCPP_TEMPLATE_VIS basic_ofstream;
                               ^
/Users/anton/zilliqa/scilla-rtl/testsuite/ContrTests.cpp:162:23: error: implicit instantiation of undefined template 'std::basic_ofstream<char>'
        std::ofstream Out(PathPrefix + Input.ExpectedOutputFilename);
                      ^
/usr/local/opt/llvm@13/bin/../include/c++/v1/iosfwd:149:32: note: template is declared here
    class _LIBCPP_TEMPLATE_VIS basic_ofstream;
                               ^
2 errors generated.
make[3]: *** [testsuite/CMakeFiles/scilla-testsuite.dir/ContrTests.cpp.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [testsuite/CMakeFiles/scilla-testsuite.dir/all] Error 2
make[1]: *** [testsuite/CMakeFiles/runtests.dir/rule] Error 2
make: *** [runtests] Error 2
```

scripts/build_ci_macos.sh

@@ -3,5 +3,12 @@
 echo "Building release build with address sanitizer"
 export PATH=/usr/local/opt/llvm@13/bin:$PATH
 export LIBRARY_PATH=/usr/local/opt/jsoncpp/lib:/usr/local/opt/secp256k1/lib/ 
-cmake -B build -S . -DCMAKE_BUILD_TYPE=Release -DADDRESS_SANITIZER=1
+
+# CMAKE_C_COMPILER and CMAKE_CXX_COMPILER make cmake pick the Homebrew Clang installation
+# and not the default AppleClang compiler
+# See https://github.com/taichi-dev/taichi/issues/3578 and some links there:
+# - https://github.com/taichi-dev/taichi/pull/3379
+# - https://stackoverflow.com/questions/45933732/how-to-specify-a-compiler-in-cmake
+cmake -D CMAKE_C_COMPILER=clang -D CMAKE_CXX_COMPILER=clang++ -B build -S . -DCMAKE_BUILD_TYPE=Release -DADDRESS_SANITIZER=1
+
 cmake --build build --target runtests -j4

scripts/dbuild_ci_macos.sh

@@ -3,5 +3,12 @@
 echo "Building debug build with address sanitizer"
 export PATH=/usr/local/opt/llvm@13/bin:$PATH 
 export LIBRARY_PATH=/usr/local/opt/jsoncpp/lib:/usr/local/opt/secp256k1/lib/ 
-cmake -B build -S . -DCMAKE_BUILD_TYPE=Debug -DADDRESS_SANITIZER=1
+
+# CMAKE_C_COMPILER and CMAKE_CXX_COMPILER make cmake pick the Homebrew Clang installation
+# and not the default AppleClang compiler
+# See https://github.com/taichi-dev/taichi/issues/3578 and some links there:
+# - https://github.com/taichi-dev/taichi/pull/3379
+# - https://stackoverflow.com/questions/45933732/how-to-specify-a-compiler-in-cmake
+cmake -D CMAKE_C_COMPILER=clang -D CMAKE_CXX_COMPILER=clang++ -B build -S . -DCMAKE_BUILD_TYPE=Debug -DADDRESS_SANITIZER=1
+
 cmake --build build --target runtests -j4

testsuite/ContrTests.cpp

@@ -15,6 +15,7 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <fstream>
 #include <boost/filesystem.hpp>
 #include <boost/test/tools/output_test_stream.hpp>
 #include <boost/test/unit_test.hpp>