link libasn1c against libmath, don't ask users to do it

libasn1c is using libm[ath] symbols from REAL.c and hence should be
linked using '-lm' to carry a dynamic linker dependency itself.

We shouldn't use a pkg-config hack to ask applications to do this on
our behalf.

Change-Id: Ie107f7252eeed90233468deaef57d3cee36abdf4
2 files changed