[Vala] vala+automake bug?

[Nor Jaidi Tuah <norjaidi tuah ubd edu bn>]

Dear all,

My project (pasang-emas.sourceforge.net) uses automake,
using AM_PROG_VALAC macro in the configure.ac file.
It uses functions from Math (Math.sin, Math.hypot etc).

Recently, one user complains that upon issuing
'./configure' and 'make', he got the following error:

/usr/bin/ld: note: 'hypot@@GLIBC_2.2.5' is defined in
DSO /lib64/libm.so.6 so try adding it to the linker command line
/lib64/libm.so.6: could not read symbols: Invalid operation
collect2: error: ld returned 1 exit status
make[2]: *** [pasang-emas] Error 1

He has to manually add -lm to the Makefile to
make 'make' work.

My questions:
* Shouldn't AM_PROG_VALAC take care of adding -lm?

* Why it works on my computer? I check my Makefile,
  and there is no -lm.

I'm scratching my head now. Please help me save my hair.

Nice day,
Nor Jaidi Tuah