[C++] do not hardcode Unix Makefiles generator (#2745)

Instead, use `cmake --build`. It has been mentioned at least in cmake
3.2 documentation [1] which has been released in 2015.
This will make a build process more flexible to people who want to use
different build systems such as Ninja.

[1]: https://cmake.org/cmake/help/v3.2/manual/cmake.1.html

lang/c++/build.sh

@@ -71,10 +71,10 @@ function do_dist() {
   fi
 }
 
-(mkdir -p build; cd build; cmake --version; cmake -G "Unix Makefiles" ..)
 for target in "$@"
 do
 
+cmake -S . -B build
 case "$target" in
   lint)
     # some versions of cppcheck seem to require an explicit
@@ -83,7 +83,7 @@ case "$target" in
     ;;
 
   test)
-    (cd build && cmake -G "Unix Makefiles" -D CMAKE_BUILD_TYPE=Debug -D AVRO_ADD_PROTECTOR_FLAGS=1 .. && make && cd .. \
+    (cmake -S. -Bbuild -D CMAKE_BUILD_TYPE=Debug -D AVRO_ADD_PROTECTOR_FLAGS=1 && cmake --build build \
       && ./build/buffertest \
       && ./build/unittest \
       && ./build/CodecTests \
@@ -105,7 +105,7 @@ case "$target" in
     ;;
 
   dist)
-    (cd build && cmake -G "Unix Makefiles" -D CMAKE_BUILD_TYPE=Release ..)
+    (cd build && cmake -D CMAKE_BUILD_TYPE=Release ..)
     do_dist
     do_doc
     ;;
@@ -119,12 +119,12 @@ case "$target" in
     ;;
 
   clean)
-    (cd build && make clean)
+    (cmake --build build --target clean)
     rm -rf doc test.avro test?.df test??.df test_skip.df test_lastSync.df test_readRecordUsingLastSync.df
     ;;
 
   install)
-    (cd build && cmake -G "Unix Makefiles" -D CMAKE_BUILD_TYPE=Release .. && make install)
+    (cmake -S. -Bbuild -D CMAKE_BUILD_TYPE=Release && cmake --build build --target install)
     ;;
 
   *)