patch 8.0.0434: clang version not correctly detected

Problem:    Clang version not correctly detected.
Solution:   Adjust the configure script. (Kazunobu Kuriyama)
diff --git a/src/configure.ac b/src/configure.ac
index 1706a8d..113fad1 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -67,8 +67,8 @@
 dnl warning when that flag is passed to.  Accordingly, adjust CFLAGS based on
 dnl the version number of the clang in use.
 dnl Note that this does not work to get the version of clang 3.1 or 3.2.
-AC_MSG_CHECKING(for recent clang version)
-CLANG_VERSION_STRING=`$CC --version 2>/dev/null | sed  -n -e 's/^.*clang.*\([[0-9]][[0-9]]*\.[[0-9]][[0-9]]*\.[[0-9]][[0-9]]*\).*$/\1/p'`
+AC_MSG_CHECKING(for clang version)
+CLANG_VERSION_STRING=`$CC --version 2>/dev/null | sed  -n -e 's/^.*clang[[^0-9]]*\([[0-9]][[0-9]]*\.[[0-9]][[0-9]]*\.[[0-9]][[0-9]]*\).*$/\1/p'`
 if test x"$CLANG_VERSION_STRING" != x"" ; then
   CLANG_MAJOR=`echo "$CLANG_VERSION_STRING" | sed -n -e 's/\([[0-9]][[0-9]]*\)\.[[0-9]][[0-9]]*\.[[0-9]][[0-9]]*/\1/p'`
   CLANG_MINOR=`echo "$CLANG_VERSION_STRING" | sed -n -e 's/[[0-9]][[0-9]]*\.\([[0-9]][[0-9]]*\)\.[[0-9]][[0-9]]*/\1/p'`
@@ -79,11 +79,15 @@
   dnl change the constant 500002075 below appropriately.  To get the
   dnl integer corresponding to a version number, refer to the
   dnl definition of CLANG_VERSION above.
+  AC_MSG_CHECKING(if clang supports -fno-strength-reduce)
   if test "$CLANG_VERSION" -ge 500002075 ; then
-    CFLAGS=`echo "$CFLAGS" | sed -n -e 's/-fno-strength-reduce/ /p'`
+    AC_MSG_RESULT(no)
+    CFLAGS=`echo "$CFLAGS" | sed -e 's/-fno-strength-reduce/ /'`
+  else
+    AC_MSG_RESULT(yes)
   fi
 else
-  AC_MSG_RESULT(no)
+  AC_MSG_RESULT(N/A)
 fi
 
 dnl If configure thinks we are cross compiling, there might be something
@@ -3016,6 +3020,14 @@
 dnl end of GUI-checking
 dnl ---------------------------------------------------------------------------
 
+AC_MSG_CHECKING([for /proc/self/exe])
+if test -L "/proc/self/exe"; then
+    AC_MSG_RESULT(yes)
+    AC_DEFINE(HAVE_PROC_SELF_EXE)
+else
+    AC_MSG_RESULT(no)
+fi
+
 dnl Check for Cygwin, which needs an extra source file if not using X11
 AC_MSG_CHECKING(for CYGWIN or MSYS environment)
 case `uname` in