RFR: JDK-8162750 -D__solaris__ added twice

[Magnus Ihse Bursie]

<hsroot>/common/autoconf/flags.m4 contains duplicated code to add 
-D__solaris__ to the JDK compiler flags when the target os is solaris.

Probably a result of a merge error during development of the new hotspot 
build system.

Bug: https://bugs.openjdk.java.net/browse/JDK-8162750
Patch inline:
diff --git a/common/autoconf/flags.m4 b/common/autoconf/flags.m4
--- a/common/autoconf/flags.m4
+++ b/common/autoconf/flags.m4
@@ -815,11 +815,6 @@
      $2CXXFLAGS_JDK="${$2CXXFLAGS_JDK} -D__solaris__"
    fi

-  if test "x$OPENJDK_TARGET_OS" = xsolaris; then
-    $2CFLAGS_JDK="${$2CFLAGS_JDK} -D__solaris__"
-    $2CXXFLAGS_JDK="${$2CXXFLAGS_JDK} -D__solaris__"
-  fi
-
    $2CFLAGS_JDK="${$2CFLAGS_JDK} ${$2EXTRA_CFLAGS}"
    $2CXXFLAGS_JDK="${$2CXXFLAGS_JDK} ${$2EXTRA_CXXFLAGS}"
    $2LDFLAGS_JDK="${$2LDFLAGS_JDK} ${$2EXTRA_LDFLAGS}"

/Magnus