MONGOCRYPT-483 make CMAKE_BUILD_TYPE configurable.

[kevinAlbs]

Summary

• add LIBMONGOCRYPT_BUILD_TYPE option to make CMAKE_BUILD_TYPE configurable.

Background & Motivation

This is motivated by updating libmongocrypt to support decimal128 Range Index CDRIVER-4394.

The C driver currently builds libmongocrypt by invoking cmake directly in compile-unix.sh and compile-windows.sh. Here is the snippet from compile-windows.sh:

   git clone --depth=1 https://github.com/mongodb/libmongocrypt --branch 1.7.0-alpha1
   mkdir libmongocrypt/cmake-build
   cd libmongocrypt/cmake-build
   "$CMAKE" -G "$CC" "-DCMAKE_PREFIX_PATH=${INSTALL_DIR}/lib/cmake" -DENABLE_SHARED_BSON=ON -DCMAKE_INSTALL_PREFIX="$INSTALL_DIR" ../
   "$CMAKE" --build . --target INSTALL --config $BUILD_CONFIG -- $BUILD_FLAGS
   cd ../../

#522 (comment) notes the required version of cmake to build libmongocrypt is cmake will soon be 3.12.0. The C driver builds with older versions of cmake in some distros. libmongocrypt's ensure-cmake.sh script ensures the presence of a CMake executable matching a specific version. Therefore, the C driver will transition to building libmongocrypt using the compile.sh script (as is currently done in the Go driver). Here is a proposed change in compile-windows.sh

   git clone https://github.com/kevinAlbs/libmongocrypt --branch decimal128_with_BUILD_CONFIG
   MONGOCRYPT_INSTALL_PREFIX=$INSTALL_DIR \
   DEFAULT_BUILD_ONLY=true \
   LIBMONGOCRYPT_EXTRA_CMAKE_FLAGS="-DBUILD_VERSION=1.7.0-pre" \
   LIBMONGOCRYPT_BUILD_TYPE=$BUILD_CONFIG \
      ./libmongocrypt/.evergreen/compile.sh

Adding the LIBMONGOCRYPT_BUILD_TYPE option enables the C driver to continue building libmongocrypt with the same CMAKE_BUILD_TYPE as the C driver.