allow out of tree builds

[yannick]

currently its not possible to do out of tree builds this makes it hard to include librdkafka with other build systems such as cmake.

/my/proj/build/librdkafka-prefix/src/librdkafka/configure --prefix=/my/proj/build/librdkafka-prefix results in

/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 19: mkl_in_list: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 21: mkl_in_list: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 22: mkl_in_list: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 27: mkl_check_terminal_color_support: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 39: mkl_require: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 42: mkl_require: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 45: mkl_require: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 93: mkl_env_esc: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 95: mkl_func_exists: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 96: mkl_err: command not found
/my/proj/build/librdkafka-prefix/src/librdkafka/configure: line 97: mkl_usage: command not found

[edenhill]

Yep, this should be added to mklove:
edenhill/mklove#17

[edenhill]

There is now cmake support