build: use LT_INIT([pic-only]) instead of forcing -fPIC in AM_CFLAGS.

Also contextually remove the AC_PROG_LIBTOOL call (which is an
obsolete name for what is now LT_INIT).

Signed-off-by: Diego Elio Pettenò <flameeyes@flameeyes.eu>
diff --git a/src/input/Makefile.am b/src/input/Makefile.am
index 9937465..309fe9d 100644
--- a/src/input/Makefile.am
+++ b/src/input/Makefile.am
@@ -1,7 +1,7 @@
 noinst_LTLIBRARIES = libosmoabis-input.la
 
 INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
-AM_CFLAGS= -fPIC -Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(COVERAGE_CFLAGS)
+AM_CFLAGS= -Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(COVERAGE_CFLAGS)
 AM_LDFLAGS = $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS) $(COVERAGE_LDFLAGS)
 
 libosmoabis_input_la_SOURCES  = dahdi.c		\