Only compile fbsd-thread.c on amd64 and i386, other architectures

have not been tested yet.

gnu/usr.bin/gdb/libgdb/Makefile

@@ -37,10 +37,14 @@ SRCS=	annotate.c arch-utils.c auxv.c ax-gdb.c ax-general.c bcache.c	\
 	tui-stack.c tui-win.c tui-windata.c tui-wingeneral.c		\
 	tui-winsource.c typeprint.c ui-file.c ui-out.c user-regs.c	\
 	utils.c valarith.c valops.c valprint.c values.c varobj.c	\
-	wrapper.c fbsd-threads.c ${LIBSRCS}
+	wrapper.c ${LIBSRCS}
 
 GENSRCS= version.c
 
+.if ${MACHINE_ARCH} == "amd64" || ${MACHINE_ARCH} == "i386"
+LIBSRCS+= fbsd-threads.c
+.endif
+
 version.c:
 	echo '#include "version.h"' >  ${.TARGET}
 	echo 'const char version[] = ${VERSION};' >> ${.TARGET}