Fix installing using build-aux/install-sh

FossilOrigin-Name: 3a8b331cffbb7ec79c016e46b9e45f65bc6c52bdff2c345c7f29ebf3685b11e3

build-aux/m4/buildsys.m4

@@ -36,6 +36,13 @@ AC_DEFUN([BUILDSYS_INIT], [
 		;;
 	esac
 
+	AC_PROG_INSTALL
+	case "$INSTALL" in
+	./build-aux/install-sh*)
+		INSTALL="$PWD/$INSTALL"
+		;;
+	esac
+
 	AC_CONFIG_COMMANDS_PRE([
 		AS_IF([test x"$GCC" = x"yes"],
 			[AC_SUBST(DEP_CFLAGS, '-MD -MF $${out%.o}.dep')])

configure.ac

@@ -25,7 +25,6 @@ BUILDSYS_INIT
 dnl If your package uses C, you want a C compiler and a C preprocessor
 AC_PROG_CC
 AC_PROG_CPP
-AC_PROG_INSTALL
 
 dnl The buildsys might require ln -s to install libraries.
 dnl Uncomment if you are compiling a library.