Let autoconf determine module include flag (typically -I)

configure.ac

@@ -15,6 +15,7 @@ AC_LANG([Fortran])
 AC_PROG_FC
 AC_FC_LIBRARY_LDFLAGS
 AC_FC_FREEFORM
+AC_FC_MODULE_FLAG
 AC_OPENMP
 
 AC_LANG([C])
@@ -84,6 +85,7 @@ AC_SUBST([API_VERSION])
 AC_SUBST([FTIMINGS_SO_VERSION], [$API_VERSION:0:0])
 AC_SUBST([AM_CFLAGS])
 AC_SUBST([AM_FCFLAGS])
+AC_SUBST([FC_MODINC])
 AC_SUBST([AM_LDFLAGS])
 AC_SUBST([DOXYGEN_OUTPUT_DIR], [docs])
 

ftimings.pc.in

@@ -8,4 +8,6 @@ Description: ftimings, API version @API_VERSION@ for Fortran compiler @FC@
 Version: @PACKAGE_VERSION@
 URL: @PACKAGE_URL@
 Libs: -L${libdir} -lftimings-@API_VERSION@-@FCNAME@ @LIBS@
-fcflags= -I${includedir}/ftimings-@API_VERSION@-@FCNAME@
+Cflags: -I${includedir}/ftimings-@API_VERSION@-@FCNAME@
+fcflags= @FC_MODINC@${includedir}/ftimings-@API_VERSION@-@FCNAME@
+fclibs= @FCLIBS@

ftimings_perflib.pc.in

@@ -9,4 +9,6 @@ Version: @PACKAGE_VERSION@
 URL: @PACKAGE_URL@
 Requires: @PACKAGE_NAME@-@API_VERSION@-@FCNAME@
 Libs: -L${libdir} -lftimings_perflib-@API_VERSION@-@FCNAME@
-fcflags= -I${includedir}/ftimings-@API_VERSION@-@FCNAME@
+Cflags: -I${includedir}/ftimings-@API_VERSION@-@FCNAME@
+fcflags= @FC_MODINC@${includedir}/ftimings-@API_VERSION@-@FCNAME@
+fclibs= @FCLIBS@