make walltimer_c part of the library

Makefile.am

@@ -5,6 +5,8 @@ lib_LTLIBRARIES = libsharp.la
 libsharp_la_SOURCES = \
   c_utils/c_utils.c \
   c_utils/c_utils.h \
+  c_utils/walltime_c.c \
+  c_utils/walltime_c.h \
   pocketfft/pocketfft.c \
   pocketfft/pocketfft.h \
   libsharp/sharp.c \
@@ -48,7 +50,7 @@ EXTRA_DIST = \
   runtest.sh
 
 check_PROGRAMS = sharp_testsuite
-sharp_testsuite_SOURCES = libsharp/sharp_testsuite.c c_utils/memusage.c c_utils/memusage.h c_utils/walltime_c.c c_utils/walltime_c.h
+sharp_testsuite_SOURCES = libsharp/sharp_testsuite.c c_utils/memusage.c c_utils/memusage.h
 sharp_testsuite_LDADD = libsharp.la
 
 TESTS = runtest.sh