add Musl support

[zg]

Projects that depend on swift-kafka-client which want to leverage the Static Linux SDK to build static executables are currently not able to as there are failures.

Example compilation failure from within the Swift Docker image attempting to compile a Swift project that depends on swift-kafka-client:

/root/.cache/checkouts/swift-kafka-client/Sources/Crdkafka/librdkafka/src/rdkafka_sasl_cyrus.c:47:10: fatal error: 'sasl/sasl.h' file not found
        47 | #include <sasl/sasl.h>
           |          ^~~~~~~~~~~~~
     1 error generated.