Don't use Batch scripts to compile for MinGW

Batch scripting is fraught with peril and will almost never do what
one expects. Any other scripting language is preferable. Since we have
Bash available and the tools to properly convert paths, just use Bash
to do this work.

Author: vector-of-bool

.evergreen/scripts/compile-windows-mingw.bat

@@ -79,18 +79,6 @@ fi
 declare -a extra_configure_flags
 IFS=' ' read -ra extra_configure_flags <<<"${EXTRA_CONFIGURE_FLAGS:-}"
 
-if [[ "${CC}" =~ mingw ]]; then
-  # MinGW has trouble compiling src/cpp-check.cpp without some assistance.
-  configure_flags_append "-DCMAKE_CXX_STANDARD=11"
-
-  env \
-    CONFIGURE_FLAGS="${configure_flags[*]} ${extra_configure_flags[*]}" \
-    INSTALL_DIR="${install_dir}" \
-    NJOBS="$(nproc)" \
-    cmd.exe /c "$(native-path "${script_dir}/compile-windows-mingw.bat")"
-  exit
-fi
-
 declare build_config
 
 if [[ "${RELEASE}" == "ON" ]]; then
@@ -112,6 +100,27 @@ fi
 
 "${cmake_binary:?}" --version
 
+if [[ "${CC}" =~ mingw ]]; then
+  # MinGW has trouble compiling src/cpp-check.cpp without some assistance.
+  configure_flags_append "-DCMAKE_CXX_STANDARD=11"
+  cmake_binary=$(native-path "$cmake_binary")
+
+  build_dir=$(native-path "$mongoc_dir")
+  env \
+    "CC=gcc" \
+    "CXX=g++" \
+    "$cmake_binary" \
+      -G "MinGW Makefiles" \
+      -D CMAKE_PREFIX_PATH="$(native-path "$install_dir/lib/cmake")" \
+      "${configure_flags[@]}" \
+      "${extra_configure_flags[@]}" \
+      -B "$build_dir" \
+      -S "$(native-path "$mongoc_dir")"
+
+  env "$cmake_binary" --build "$build_dir" --parallel "$(nproc)"
+  exit 0
+fi
+
 declare compile_flags=(
   "/m" # Number of concurrent processes. No value=# of cpus
 )