Use PKG_CHECK_MODULES to locate libusb-1.0.

This works better on FreeBSD.

.gitignore

@@ -1,4 +1,5 @@
 /configure
+/aclocal.m4
 bld/*/*.h
 bld/*/*.o
 bld/*/dpimp

.travis.yml

@@ -1,7 +1,7 @@
 language: c
 dist: trusty
 sudo: required
-install: sudo apt-get install libusb-1.0-0-dev
+install: sudo apt-get install libusb-1.0-0-dev pkg-config
 script:
   - ./autogen.sh
   - mkdir tmp

autogen.sh

@@ -19,6 +19,7 @@ builddir=$(pwd)
 cd "$srcdir"
 srcdir=$(pwd)
 
+aclocal         # creates aclocal.m4 from configure.ac
 autoconf	# creates configure from configure.ac
 autoheader	# creates src/config.h.in from configure.ac
 

configure.ac

@@ -103,15 +103,10 @@ AC_CHECK_FUNC([nanosleep],
 case "${need_libusb}" in
     yes)
         # Check if libusb-1.0 is present, otherwise fail.
-        # CPULIBS is for libraries only needed by the CPU, not by other programs.
-        SAVE_LIBS="$LIBS"
-        LIBS=""
-        AC_CHECK_LIB([usb-1.0], [libusb_get_device_descriptor],
-                     [],
-                     [AC_MSG_ERROR([Lights require libusb-1.0, which I could not find.])]
-                    )
-        CPULIBS="$LIBS"
-        LIBS="$SAVE_LIBS"
+        PKG_CHECK_MODULES([libusb], [libusb-1.0],
+                          [AC_DEFINE([HAVE_LIBUSB_1_0], [1],
+                                     [Define if you have libusb-1.0.])],
+                          [AC_MSG_ERROR([Lights require libusb-1.0, which I could not find.])])
         ;;
 esac
 
@@ -287,6 +282,8 @@ AC_SUBST([CPULIBS])
 AC_SUBST([NETLIBS])
 AC_SUBST([MAKEFILE], [Makefile])
 AC_SUBST([CENVFLAGS])
+AC_SUBST([libusb_CFLAGS])
+AC_SUBST([libusb_LIBS])
 
 # -------------------------------------------------------------------------
 # Output section. State which files are going to be constructed.

mk/top.mk

@@ -18,14 +18,14 @@
 SRC = @top_srcdir@/src
 BLDSRC = @top_builddir@/src
 CC = @CC@
-CFLAGS = -c @CFLAGS@
+CFLAGS = -c @CFLAGS@ @libusb_CFLAGS@
 CPPFLAGS = @CPPFLAGS@ -I$(BLDSRC) -I$(SRC)
 CFLAGS_LINT = -ansi -pedantic -Wall -Wshadow \
                 -Wstrict-prototypes -Wmissing-prototypes \
                 -Wmissing-declarations -Wredundant-decls
 LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@
-CPULIBS = @CPULIBS@
+CPULIBS = @CPULIBS@ @libusb_LIBS@
 NETLIBS = @NETLIBS@
 
 prefix = @prefix@

src/dvlites.c

@@ -34,7 +34,7 @@ static int decosfcclossage;
 #if KLH10_DEV_LITES		/* Moby conditional for entire file */
 
 #if HAVE_LIBUSB_1_0
-#include <libusb-1.0/libusb.h>
+#include <libusb.h>
 #endif
 /*
  * For now, assume that having <sys/io.h> is equivalent to having