properly check if -lrt and -lm is needed

Fixes build against uClibc.

uClibc provides 2 versions of clock_gettime(), one with realtime
support and one without (this is so you can avoid linking in -lrt
unless actually needed). This means that the clock_gettime() don't
need -lrt. We still need it for timer_create() so we check for this
function in addition.

We also need check if -lm is needed for isnan().


diff --git a/Makefile b/Makefile
index 1cd5bc8..f414291 100644
--- a/Makefile
+++ b/Makefile
@@ -35,7 +35,7 @@ configure: ;
 
 $(call set-vpath, $(SRC_PATH))
 
-LIBS+=-lz $(LIBS_TOOLS)
+LIBS+=-lz $(LIBS_TOOLS) $(LIBM) $(LIBRT)
 
 HELPERS-$(CONFIG_LINUX) = qemu-bridge-helper$(EXESUF)
 
@@ -172,7 +172,7 @@ fsdev/virtfs-proxy-helper$(EXESUF): LIBS += -lcap
 qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx
 	$(call quiet-command,sh $(SRC_PATH)/scripts/hxtool -h < $< > $@,"  GEN   $@")
 
-qemu-ga$(EXESUF): LIBS = $(LIBS_QGA)
+qemu-ga$(EXESUF): LIBS = $(LIBS_QGA) $(LIBRT) $(LIBM)
 qemu-ga$(EXESUF): QEMU_CFLAGS += -I qga/qapi-generated
 
 gen-out-type = $(subst .,-,$(suffix $@))
diff --git a/Makefile.target b/Makefile.target
index 7892a8d..1c3bf31 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -34,9 +34,7 @@ PROGS+=$(QEMU_PROGW)
 endif
 STPFILES=
 
-ifndef CONFIG_HAIKU
-LIBS+=-lm
-endif
+LIBS+=$(LIBM) $(LIBRT)
 
 config-target.h: config-target.h-timestamp
 config-target.h-timestamp: config-target.mak
diff --git a/configure b/configure
index d97fd81..697946c 100755
--- a/configure
+++ b/configure
@@ -126,6 +126,8 @@ audio_win_int=""
 cc_i386=i386-pc-linux-gnu-gcc
 libs_qga=""
 debug_info="yes"
+libm=""
+librt=""
 
 target_list=""
 
@@ -2666,19 +2668,43 @@ EOF
   fi
 fi
 
+##########################################
+# Do we need libm
+cat > $TMPC << EOF
+#include <math.h>
+int main(void) { return isnan(0.0); }
+EOF
+if compile_prog "" "" ; then
+  libm=
+elif compile_prog "" "-lm" ; then
+  libm="-lm"
+else
+  echo
+  echo "Error: libm check failed"
+  echo
+  exit 1
+fi
 
 ##########################################
 # Do we need librt
 cat > $TMPC <<EOF
 #include <signal.h>
 #include <time.h>
-int main(void) { return clock_gettime(CLOCK_REALTIME, NULL); }
+int main(void) {
+  timer_create(CLOCK_REALTIME, NULL, NULL);
+  return clock_gettime(CLOCK_REALTIME, NULL);
+}
 EOF
 
 if compile_prog "" "" ; then
   :
 elif compile_prog "" "-lrt" ; then
-  LIBS="-lrt $LIBS"
+  librt="-lrt"
+else
+  echo
+  echo "Error: librt check failed"
+  echo
+  exit 1
 fi
 
 if test "$darwin" != "yes" -a "$mingw32" != "yes" -a "$solaris" != yes -a \
@@ -3581,6 +3607,8 @@ echo "LIBS_TOOLS+=$libs_tools" >> $config_host_mak
 echo "EXESUF=$EXESUF" >> $config_host_mak
 echo "LIBS_QGA+=$libs_qga" >> $config_host_mak
 echo "POD2MAN=$POD2MAN" >> $config_host_mak
+echo "LIBM=$libm" >> $config_host_mak
+echo "LIBRT=$librt" >> $config_host_mak
 
 # generate list of library paths for linker script