Trying to build the RPM for Fedora 21 x86_64 with mp3 support and I get the following:
/bin/sh ../libtool --silent --tag=CC --silent --mode=link gcc -Wtraditional-conversion -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -D_FILE_OFFSET_BITS=64 -fstack-protector -Wall -W -Wmissing-prototypes -Wstrict-prototypes -pedantic -fopenmp -avoid-version -module -Wl,-z,relro -Wl,-z,defs -o libsox_fmt_wavpack.la -rpath /usr/lib64/sox wavpack.lo libsox.la -lwavpack -lm
.libs/mp3.o: In function startread':
/home/build/rpmbuild/sox/BUILD/sox-14.4.2/src/mp3.c:407: undefined reference tolsx_error'
collect2: error: ld returned 1 exit status
Makefile:1287: recipe for target 'libsox_fmt_mp3.la' failed
I ended up fixing this (and flac) building dynamically by exporting lsx_error and lsx_flush.