RFR: JDK-8240950 Missing AC_SUBST after JDK-82408

[Magnus Ihse Bursie]

Unfortunately two babies went out with the bathwaters. This restores 
functionality for smartjavac and javac-server.

Bug: https://bugs.openjdk.java.net/browse/JDK-8240950
Patch inline:
diff --git a/make/autoconf/build-performance.m4 
b/make/autoconf/build-performance.m4
--- a/make/autoconf/build-performance.m4
+++ b/make/autoconf/build-performance.m4
@@ -447,12 +447,14 @@
        CHECKING_MSG: [whether to use sjavac],
        IF_ENABLED: [ ENABLE_SJAVAC="yes" ],
        IF_DISABLED: [ ENABLE_SJAVAC="no" ])
+  AC_SUBST(ENABLE_SJAVAC)

    UTIL_ARG_ENABLE(NAME: javac-server, DEFAULT: true, AVAILABLE: 
$JAVAC_SERVER_AVAILABLE,
        DESC: [enable javac server],
        CHECKING_MSG: [whether to use javac server],
        IF_ENABLED: [ ENABLE_JAVAC_SERVER="yes" ],
        IF_DISABLED: [ ENABLE_JAVAC_SERVER="no" ])
+  AC_SUBST(ENABLE_JAVAC_SERVER)

    if test "x$ENABLE_JAVAC_SERVER" = "xyes" || test "x$ENABLE_SJAVAC" = 
"xyes"; then
      # When using a server javac, the small client instances do not 
need much

/Magnus