Link with libc++ on FreeBSD.

Author: gwright83

double-conversion.cabal

@@ -72,7 +72,7 @@ library
   if impl(ghc >= 9.4)
     build-depends: system-cxx-std-lib == 1.0
 
-  elif os(darwin)
+  elif os(darwin) || os(freebsd)
     extra-libraries: c++
   elif os(windows)
     if arch(x86_64) && impl(ghc < 8.6.5)