build: use libbsd when using OSS and glibc

Some systems offer OSS v4 but do not have BSD-only functions like
strlcpy, used in cubeb_oss.c. An example is Debian GNU/kFreeBSD, that
uses a FreeBSD kernel with GNU userspace utilities, like glibc.

With this patch cubeb will be able to build on these systems thanks to
the help of libbsd, that privides most libc functions that you would
expect on BSD.

CMakeLists.txt

@@ -284,9 +284,22 @@ if(HAVE_SYS_SOUNDCARD_H)
   try_compile(USE_OSS "${PROJECT_BINARY_DIR}/compile_tests"
     ${PROJECT_SOURCE_DIR}/cmake/compile_tests/oss_is_v4.c)
   if(USE_OSS)
-    target_sources(cubeb PRIVATE
-      src/cubeb_oss.c)
-    target_compile_definitions(cubeb PRIVATE USE_OSS)
+    # strlcpy is not available on BSD systems that use glibc,
+    # like Debian kfreebsd, so try using libbsd if available
+    include(CheckSymbolExists)
+    check_symbol_exists(strlcpy string.h HAVE_STRLCPY)
+    if(NOT HAVE_STRLCPY)
+      pkg_check_modules(libbsd-overlay IMPORTED_TARGET libbsd-overlay)
+      if(libbsd-overlay_FOUND)
+        target_link_libraries(cubeb PRIVATE PkgConfig::libbsd-overlay)
+        set(HAVE_STRLCPY true)
+      endif()
+    endif()
+    if (HAVE_STRLCPY)
+      target_sources(cubeb PRIVATE
+        src/cubeb_oss.c)
+      target_compile_definitions(cubeb PRIVATE USE_OSS)
+    endif()
   endif()
 endif()