uclibc/defconfig: enable XSI math

ARM926 size delta +12 KB.
It's required for the upcoming mpv package.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/uclibc/uClibc-ng.config

@@ -1,4 +1,5 @@
 DO_C99_MATH=y
+DO_XSI_MATH=y
 KERNEL_HEADERS="/usr/src/linux/include"
 # LDSO_CACHE_SUPPORT is not set
 # UCLIBC_STATIC_LDCONFIG is not set