Fix build for NetBSD (and presumably DragonFly BSD)

These both use POSIX threads. I got a link error when cross-compiling
using Nixpkgs (Linux -> NetBSD) that went away once I passed `-pthread`.

The autoconf is crafted to have the same conditional as the C code itself.

CMakeLists.txt

@@ -21,6 +21,18 @@ option(LIBCPUID_TESTS "Enable building tests" OFF)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_C_STANDARD 99)
 
+# pthreads library
+if(${CMAKE_SYSTEM_NAME} STREQUAL "DragonFly" OR ${CMAKE_SYSTEM_NAME} STREQUAL "NetBSD")
+  find_package(Threads REQUIRED)
+endif()
+
+# check if popcount64 is available
+include(CheckSymbolExists)
+check_symbol_exists(popcount64 "string.h" HAVE_POPCOUNT64)
+if(HAVE_POPCOUNT64)
+  add_definitions(-DHAVE_POPCOUNT64)
+endif(HAVE_POPCOUNT64)
+
 # Global variables
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 

configure.ac

@@ -62,18 +62,45 @@ fi
 
 AC_CANONICAL_HOST
 
+AC_MSG_CHECKING([Whether we need POSIX threads])
+AC_COMPILE_IFELSE([
+    AC_LANG_PROGRAM([
+        #if defined(__NetBSD__) || defined(__DragonFly__)
+        #else
+        #  error "no pthreads needed"
+        #endif
+    ])
+], [
+    AC_MSG_RESULT([yes])
+    AC_SUBST([LIBCPUID_LDFLAGS], ["-pthread"])
+], [
+    AC_MSG_RESULT([no])
+])
+
 build_windows=no
+build_netbsd=no
+build_dragonflybsd=no
 
 case "${host_os}" in
     cygwin*|mingw*)
         build_windows=yes
         ;;
+    netbsd*)
+        build_netbsd=yes
+        ;;
+    dragonfly*)
+        build_dragonflybsd=yes
+        ;;
 esac
 
 if test "$build_windows" = "no"; then
     AM_CPPFLAGS="$AM_CPPFLAGS -D_GNU_SOURCE"
 fi
 
+if test "$build_netbsd" = "yes" || test "$build_dragonflybsd" = "yes"; then
+    AM_LDFLAGS="$AM_LDFLAGS -pthread"
+fi
+
 AM_CONDITIONAL([WINDOWS], [test "$build_windows" = "yes"])
 
 AC_SUBST(AM_CPPFLAGS)

libcpuid/CMakeLists.txt

@@ -23,6 +23,7 @@ add_library(cpuid ${cpuid_sources})
 set_property(TARGET cpuid PROPERTY WINDOWS_EXPORT_ALL_SYMBOLS ON)
 target_include_directories(cpuid SYSTEM PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
 
+target_link_libraries(cpuid ${CMAKE_THREAD_LIBS_INIT})
 target_compile_definitions(cpuid PRIVATE VERSION="${PROJECT_VERSION}")
 set_target_properties(cpuid PROPERTIES VERSION "${LIBCPUID_CURRENT}.${LIBCPUID_AGE}.${LIBCPUID_REVISION}")
 set_target_properties(cpuid PROPERTIES SOVERSION "${LIBCPUID_CURRENT}")