Add rt lib linkage to enable use of clock_nanosleep functions with older glibc.

Makefile.am

@@ -25,7 +25,7 @@ bin_SCRIPTS	= $(top_srcdir)/*.cl
 cgminer_LDFLAGS	= $(PTHREAD_FLAGS)
 cgminer_LDADD	= $(DLOPEN_FLAGS) @LIBCURL_LIBS@ @JANSSON_LIBS@ @PTHREAD_LIBS@ \
 		  @OPENCL_LIBS@ @NCURSES_LIBS@ @PDCURSES_LIBS@ @WS2_LIBS@ \
-		  @LIBUSB_LIBS@ @MM_LIBS@ \
+		  @LIBUSB_LIBS@ @MM_LIBS@ @RT_LIBS@ \
 		  @MATH_LIBS@ lib/libgnu.a ccan/libccan.a
 
 if HAVE_WINDOWS

configure.ac

@@ -67,6 +67,7 @@ OPENCL_LIBS="-lOpenCL"
 WS2_LIBS=""
 MM_LIBS=""
 MATH_LIBS="-lm"
+RT_LIBS="-lrt"
 
 case $target in
   amd64-*)
@@ -421,6 +422,7 @@ AC_SUBST(PDCURSES_LIBS)
 AC_SUBST(WS2_LIBS)
 AC_SUBST(MM_LIBS)
 AC_SUBST(MATH_LIBS)
+AC_SUBST(RT_LIBS)
 AC_SUBST(ADL_CPPFLAGS)
 
 AC_CONFIG_FILES([