Fix incorrect and nonstandard use of error()

[nmlgc]

The error() function is defined nowhere in this codebase. When linking against glibc, the declaration will match the nonstandard error(3) function, but midicomp only ever passes a single const char* to this function, which doesn't match its 3+-parameter signature. Consequently, this code fails to link with any other libc, and doesn't correctly show the respective errors even with glibc.

Using prs_error() fixes these issues, allows this code to be compiled with MinGW, and retains the line number in the now correct error output.