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

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

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

MANIFEST

@@ -16,6 +16,7 @@ dwarves_reorganize.c
 dwarves_reorganize.h
 cmake/modules/FindDWARF.cmake
 cmake/modules/Findargp.cmake
+cmake/modules/Findobstack.cmake
 CMakeLists.txt
 codiff.c
 ctracer.c

cmake/modules/Findobstack.cmake

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