[libc++] Fix missing macro definition for lgamma (#157610)

Author: jhuber6

libcxx/include/__random/binomial_distribution.h

@@ -101,6 +101,8 @@ class binomial_distribution {
 #if defined(_LIBCPP_GLIBC_PREREQ)
 #  if _LIBCPP_GLIBC_PREREQ(2, 8)
 #    define _LIBCPP_LGAMMA_R_NOEXCEPT _NOEXCEPT
+#  else
+#    define _LIBCPP_LGAMMA_R_NOEXCEPT
 #  endif
 #elif defined(__LLVM_LIBC__)
 #  define _LIBCPP_LGAMMA_R_NOEXCEPT _NOEXCEPT