Specifically, bring in maths library through AC_SEARCH_LIBS and add
checks for sqrt() and pow() only after we've established which library
might contain these functions. Similarly, rely on AC_SEARCH_LIBS
adding -lamd to ${LIBS} if needed in which case it is not necessary to
manually bring these libraries in while searching for UMFPACK.
Finally, add check for memset(). Needed by Tarjan implementation.
Specifically, we don't (currently) use per-target compilation or
linking flags, and therefore do not need a portability aid in our
current build process.
Automake 1.11 introduced the concept of "silent build rules" wherein the
build commands are reported as
CC spu_explicit.lo
rather than something along the lines of
/bin/bash ../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I../../../../../opmtransport/src -I.. -O3 -DNDEBUG -Wall -Wextra -std=c99 -pedantic -march=native -mtune=native -MT spu_explicit.lo -MD -MP -MF .deps/spu_explicit.Tpo -c -o spu_explicit.lo ../../../../../opmtransport/src/spu_explicit.c
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I../../../../../opmtransport/src -I.. -O3 -DNDEBUG -Wall -Wextra -std=c99 -pedantic -march=native -mtune=native -MT spu_explicit.lo -MD -MP -MF .deps/spu_explicit.Tpo -c ../../../../../opmtransport/src/spu_explicit.c -fPIC -DPIC -o .libs/spu_explicit.o
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I../../../../../opmtransport/src -I.. -O3 -DNDEBUG -Wall -Wextra -std=c99 -pedantic -march=native -mtune=native -MT spu_explicit.lo -MD -MP -MF .deps/spu_explicit.Tpo -c ../../../../../opmtransport/src/spu_explicit.c -o spu_explicit.o >/dev/null 2>&1
The former is much easier to read and, consequently, more conducive to
visually noticing diagnostics from the toolset (compiler, linker &c).
On the other hand, only fairly recent editions of Automake have the
"silent rule" capability, so enable silent rules only if available. In
particular, Automake 1.10.x (the default Automake version in MacOS X
10.6) does not support the capability. Neither does the default
Automake in CentOS 5.6.
Further details on silent build rules can be found at
http://sources.redhat.com/automake/automake.html#Optionshttp://www.flameeyes.eu/autotools-mythbuster/automake/silent.html
Thanks to Arne Morten Kvarving in Dune Flyspray issue #922
(http://www.dune-project.org/flyspray/index.php?do=details&task_id=922)
for the tip on how to preserve "configure.ac" backwards compatibility
with Automake < 1.11 .
