meson.build: Fixes for *BSD

Add NetBSD and OpenBSD. FreeBSD and OpenBSD use libc++.

Author: brad0

meson.build

@@ -57,7 +57,7 @@ cpp_lib = '-lstdc++'
 libm_dep = cpp.find_library('m', required : false)
 deps += [libm_dep]
 
-if ['linux', 'freebsd', 'android', 'ios', 'darwin'].contains(system)
+if ['linux', 'android', 'ios', 'darwin', 'freebsd', 'netbsd', 'openbsd'].contains(system)
   asm_format32 = 'elf'
   asm_format64 = 'elf64'
   if ['ios', 'darwin'].contains(system)
@@ -109,7 +109,7 @@ if ['linux', 'freebsd', 'android', 'ios', 'darwin'].contains(system)
     error('FIXME: unhandled CPU family @0@ for @1@'.format(cpu_family, system))
   endif
 
-  if ['ios', 'darwin', 'android'].contains(system)
+  if ['ios', 'darwin', 'android', 'freebsd', 'openbsd'].contains(system)
     cpp_lib = '-lc++'
   endif
 elif system == 'windows'