Don't use pkg-config to check for libev

Several distributions used to ship a .pc file for libev, but upstream has
ultimately rejected supporting pkg-config. This is causing distros to
remove support for libev.

configure.ac

@@ -146,8 +146,14 @@ if test x$WITH_GLIB != xno; then
 fi
 
 if test x$WITH_LIBEV != xno; then
-  PKG_CHECK_MODULES([libev], [libev], [BUILD_LIBEV=$WITH_LIBEV],
-                    [test x$WITH_LIBEV != xauto && AC_MSG_ERROR("libev not found")])
+  AC_CHECK_HEADER(
+    [ev.h],
+    AC_CHECK_LIB(
+      [ev], [ev_loop_new], [BUILD_LIBEV=$WITH_LIBEV],
+      [test x$WITH_LIBEV != xauto && AC_MSG_ERROR("libev not found")]
+    ),
+    [test x$WITH_LIBEV != xauto && AC_MSG_ERROR("ev.h not found")]
+  )
   if test x$BUILD_LIBEV == xauto; then
     BUILD_LIBEV=yes
   fi

src/Makefile.am

@@ -43,8 +43,8 @@ lib_LTLIBRARIES += libverto-libev.la
 include_HEADERS += verto-libev.h
 libverto_libev_la_SOURCES = verto-libev.c
 libverto_libev_la_LIBADD  = libverto.la
-libverto_libev_la_CFLAGS  = $(AM_CFLAGS) $(libev_CFLAGS)
-libverto_libev_la_LDFLAGS = $(AM_LDFLAGS) $(libev_LIBS) \
+libverto_libev_la_CFLAGS  = $(AM_CFLAGS)
+libverto_libev_la_LDFLAGS = $(AM_LDFLAGS) -lev \
                             -export-symbols $(srcdir)/libverto-libev.symbols
 endif