RFR: JDK-8180897 Explicit --with-jtreg path not expanded

[Magnus Ihse Bursie]

 From the bug report:

When configuring with --with-jtreg=<path>, the provided path doesn't 
appear to be expanded. Thus, my use of --with-jtreg=~/devtools/jtreg 
fails and reports "~/devtools/jtreg" doesn't exist.

The intention is to push this once the consolidated forest opens.

Bug: 
https://bugs.openjdk.java.net/browse/JDK-8180897-handle-relative-jtreg-path
Patch inline:
diff --git a/make/autoconf/toolchain.m4 b/make/autoconf/toolchain.m4
--- a/make/autoconf/toolchain.m4
+++ b/make/autoconf/toolchain.m4
@@ -935,6 +935,7 @@
    elif test "x$with_jtreg" != xyes && test "x$with_jtreg" != x; then
      # An explicit path is specified, use it.
      JT_HOME="$with_jtreg"
+    BASIC_FIXUP_PATH([JT_HOME])
      if test ! -d "$JT_HOME"; then
        AC_MSG_ERROR([jtreg home directory from --with-jtreg=$with_jtreg 
does not exist])
      fi

/Magnus