Bug#51607: Automake distcheck target broken.

Reason for the error was that ./configure wrapper script was  not 
safe for VPATH builds used by "make distcheck", specifically it expected configure.am to be in the current directory.

Fix changes configure wrapper to resolve script names relative 
to configure script path.

Also, use $top_srcdir/configure.am instead of configure.am in dist-hook to be more VPATH friendly.

BUILD/choose_configure.sh

@@ -5,10 +5,11 @@
 # Ensure cmake and perl are there
 cmake -P cmake/check_minimal_version.cmake >/dev/null 2>&1 || HAVE_CMAKE=no
 perl --version >/dev/null 2>&1 || HAVE_CMAKE=no
+scriptdir=`dirname $0`
 if test "$HAVE_CMAKE" = "no"
 then
-  sh ./configure.am "$@"
+  sh $scriptdir/configure.am "$@"
 else
-  perl ./cmake/configure.pl "$@"
+  perl $scriptdir/cmake/configure.pl "$@"
 fi
 

Makefile.am

@@ -60,7 +60,8 @@ dist-hook:
 		--datadir=$(distdir)/win/data \
 		--srcdir=$(top_srcdir)
 	storage/myisam/myisamchk --silent --fast $(distdir)/win/data/mysql/*.MYI
-	test ! -f configure.am  || $(INSTALL_DATA)  configure.am $(distdir)
+	test ! -f $(top_srcdir)/configure.am  || \
+	$(INSTALL_DATA)  $(top_srcdir)/configure.am $(distdir)
 
 all-local:		@ABI_CHECK@