cmake: add pkg-config pc file generation

Create libperiphery.pc file for pkg-config. Allows to use
PKG_CHECK_MODULE in cmake, meson or autotools projet.

Example with cmake:
In CMakeLists:
pkg_check_modules(CPERIPHERY libperiphery REQUIRED)

-- Checking for module 'libperiphery'
--   Found libperiphery, version 2.1.0

Signed-off-by: Joris Offouga <offougajoris@gmail.com>

Rebase to use fixed variable names and updated cmake project name.
Also, rearrange some definitions in CMakeLists.txt.

Resolves #21.

Signed-off-by: Vanya A. Sergeev <v@sergeev.io>

CMakeLists.txt

@@ -34,9 +34,20 @@ include_directories(${CMAKE_CURRENT_SOURCE_DIR}/src)
 add_library(periphery ${periphery_SOURCES} ${periphery_HEADERS})
 set_target_properties(periphery PROPERTIES SOVERSION ${VERSION})
 
+include(GNUInstallDirs)
+
+set(prefix      ${CMAKE_INSTALL_PREFIX})
+set(exec_prefix ${CMAKE_INSTALL_PREFIX})
+set(includedir  ${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR})
+set(libdir      ${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR})
+
+# Generate pkg-config pc file
+configure_file(${CMAKE_SOURCE_DIR}/src/libperiphery.pc.in ${CMAKE_BINARY_DIR}/libperiphery.pc @ONLY)
+
 # Declare install targets
-install(TARGETS periphery DESTINATION lib)
-install(FILES ${periphery_HEADERS} DESTINATION include/${PROJECT_NAME})
+install(TARGETS periphery DESTINATION ${CMAKE_INSTALL_LIBDIR})
+install(FILES ${periphery_HEADERS} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME})
+install(FILES ${CMAKE_BINARY_DIR}/libperiphery.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
 
 # Declare tests targets
 foreach(TEST_SOURCE ${periphery_TESTS})

src/libperiphery.pc.in

@@ -0,0 +1,10 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: libperiphery
+Description: Library for peripheral I/O (GPIO, LED, PWM, SPI, I2C, MMIO, Serial) in Linux
+Version: @VERSION@
+Libs: -L${libdir} -lperiphery
+Cflags: -I${includedir}