[RFR] JDK-8156980: Hotspot build doesn't have -std=gnu++98 gcc option

[Andrew Hughes]

Webrev: http://cr.openjdk.java.net/~andrew/8156980/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8156980

With "8151841: Build needs additional flags to compile with GCC 6",
we added a number of compiler flags which were needed to build
OpenJDK with GCC 6. Checks for these flags were added to configure,
and the flags passed to the JDK and HotSpot builds by CFLAGS/CXXFLAGS_JDK
and hotspot-spec.gmk.in respectively.

Following "8152666: The new Hotspot Build System" and
"8150601: Remove the old Hotspot build system", the hotspot-spec.gmk.in
file was removed, so the flags were no longer passed to the HotSpot
build. HotSpot now uses JVM_CFLAGS via the same configure process
as the JDK obtains CFLAGS_JDK and CXXFLAGS_JDK[*].

This webrev fixes the regression introduced by 8152666 by adding
the flags to JVM_CFLAGS. It also adapts FLAGS_SETUP_GCC6_COMPILER_FLAGS
to take a prefix, as other macros in flags.m4 do, and calls
TOOLCHAIN_PREPARE_FOR_VERSION_COMPARISONS before the version check.
The lack of the latter lead to configure executing:

if test $OPENJDK_BUILD_COMPARABLE_ACTUAL_VERSION -ge $COMPARABLE_REFERENCE_VERSION

with OPENJDK_BUILD_COMPARABLE_ACTUAL_VERSION ever being set, causing
test to print an error.

With this fix, the flags again make it into the build.

[*] It should really be CXXFLAGS_JVM as they are flags for the C++ compiler.
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

PGP Key: ed25519/35964222 (hkp://keys.gnupg.net)
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