Merge pull request swiftlang#937 from smikes/bootstrap-ninja-set-make-program

[build-script-impl][SR-58] When bootstrapping ninja, set CMAKE_MAKE_COMMAND

Author: gribozavr

utils/build-script-impl

@@ -1327,7 +1327,11 @@ if [[ "${BUILD_NINJA}" ]] ; then
           { set +x; } 2>/dev/null
         fi
     fi
-    export PATH="${build_dir}:${PATH}"
+    NINJA_BIN="${build_dir}/ninja"
+    COMMON_CMAKE_OPTIONS=(
+        "${COMMON_CMAKE_OPTIONS[@]}"
+        -DCMAKE_MAKE_PROGRAM=${NINJA_BIN}
+    )
 fi
 
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