/usr/bin/musl-gcc is in musl-tools 1.1.19-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 | #!/bin/sh
exec "${REALGCC:-cc}" "$@" -specs /usr/share/dpkg/no-pie-compile.specs -specs /usr/share/dpkg/no-pie-link.specs -specs "/usr/lib/x86_64-linux-musl/musl-gcc.specs"
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