ppc: do not include copysgnl.c if UCLIBC_HAS_LONG_DOUBLE_MATH enabled

Fixes compilation of uClibc-ng when UCLIBC_HAS_LONG_DOUBLE_MATH is
used.

libc/sysdeps/linux/powerpc/Makefile.arch

@@ -5,7 +5,8 @@
 # Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
 #
 
-CSRC-y := __syscall_error.c ioctl.c copysignl.c
+CSRC-y := __syscall_error.c ioctl.c
+CSRC-$(if $(UCLIBC_HAS_LONG_DOUBLE_MATH),,y) += copysignl.c
 
 SSRC-y := \
 	__longjmp.S setjmp.S bsd-setjmp.S bsd-_setjmp.S brk.S \