cmake: Add a module to find if argp is in a separate library

The musl libc, used in Alpine Linux, doesn't have argp support, so check
if it is somewhere else, maybe in the argp-standalone package.

Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

MANIFEST

@@ -15,6 +15,7 @@ dwarves_fprintf.c
 dwarves_reorganize.c
 dwarves_reorganize.h
 cmake/modules/FindDWARF.cmake
+cmake/modules/Findargp.cmake
 CMakeLists.txt
 codiff.c
 ctracer.c

cmake/modules/Findargp.cmake

@@ -0,0 +1,41 @@
+# - Find argp
+# Figure out if argp is in glibc or if it argp-standalone
+#
+#  ARGP_LIBRARY     - Library to use argp
+#  ARGP_FOUND       - True if found.
+
+message(STATUS "Checking availability of argp library")
+
+INCLUDE(CheckLibraryExists)
+
+if (ARGP_LIBRARY)
+	# Already in cache, be silent
+	set(ARGP_FIND_QUIETLY TRUE)
+endif (ARGP_LIBRARY)
+
+find_library(ARGP_LIBRARY
+	NAMES argp
+	PATHS /usr/lib /usr/local/lib /usr/lib64 /usr/local/lib64 ~/usr/local/lib ~/usr/local/lib64
+)
+
+if (ARGP_LIBRARY)
+	set(ARGP_FOUND TRUE)
+	set(ARGP_LIBRARY ${ARGP_LIBRARY})
+	set(CMAKE_REQUIRED_LIBRARIES ${ARGP_LIBRARY})
+else (ARGP_LIBRARY)
+	set(ARGP_LIBRARY "")
+endif (ARGP_LIBRARY)
+
+if (ARGP_FOUND)
+	if (NOT ARGP_FIND_QUIETLY)
+		message(STATUS "Found argp library: ${ARGP_LIBRARY}")
+	endif (NOT ARGP_FIND_QUIETLY)
+else (ARGP_FOUND)
+	set(ARGP_FOUND TRUE)
+	message(STATUS "Assuming argp is in libc")
+endif (ARGP_FOUND)
+
+mark_as_advanced(ARGP_LIBRARY)
+configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.cmake ${CMAKE_CURRENT_SOURCE_DIR}/config.h)
+
+message(STATUS "Checking availability of argp library - done")