Apart from a single static mistake, there is a problem with CFLAGS. Patch attached, should also apply against new 1.15t
Created attachment 50883 [details, diff] Musepack-tools GCC 4 compile fix The flags are turned off because: A) it isn't right to enable optimisations I didn't ask for B) -fmove-all-movables is no longer supported
Created attachment 50886 [details, diff] GCC 4 compile fix The real fix w/o any additions. Applies against 1.15t cleanly.
In portage, thank you for your report. Please give the modified ebuild two hours to propagate before syncing.