merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/aclocal.m4

@@ -0,0 +1,40 @@
+dnl Check for socklen_t: historically on BSD it is an int, and in
+dnl POSIX 1g it is a type of its own, but some platforms use different
+dnl types for the argument to getsockopt, getpeername, etc.  So we
+dnl have to test to find something that will work.
+AC_DEFUN([TYPE_SOCKLEN_T],
+[
+   AC_CHECK_TYPE([socklen_t], ,[
+      AC_MSG_CHECKING([for socklen_t equivalent])
+      AC_CACHE_VAL([git_cv_socklen_t_equiv],
+      [
+         # Systems have either "struct sockaddr *" or
+         # "void *" as the second argument to getpeername
+         git_cv_socklen_t_equiv=
+         for arg2 in "struct sockaddr" void; do
+            for t in int size_t unsigned long "unsigned long"; do
+               AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
+                  #include <sys/types.h>
+                  #include <sys/socket.h>
+
+                  int getpeername (int, $arg2 *, $t *);
+               ],[
+                  $t len;
+                  getpeername(0,0,&len);
+               ])],[
+                  git_cv_socklen_t_equiv="$t"
+                  break 2
+               ])
+            done
+         done
+
+         if test "x$git_cv_socklen_t_equiv" = x; then
+            AC_MSG_ERROR([Cannot find a type to use in place of socklen_t])
+         fi
+      ])
+      AC_MSG_RESULT($git_cv_socklen_t_equiv)
+      AC_DEFINE_UNQUOTED(socklen_t, $git_cv_socklen_t_equiv,
+			[type to use in place of socklen_t if not defined])],
+      [#include <sys/types.h>
+#include <sys/socket.h>])
+])