RFR: 8234535: Cross compilation fails due to missing CFLAGS for the BUILD_CC

[christoph.goettschkes at microdoc.com]

Hi,

please review the following change.

Bug: https://bugs.openjdk.java.net/browse/JDK-8234535
Webrev: https://cr.openjdk.java.net/~cgo/8234535/webrev.00/

The removed lines are completely out of place and have no use at all. for 
the CC variable, for instance, the script does the following:

CC_OLD="$CC"
CC="$BUILD_CC"
CC="$CC_OLD"

without executing any function between those lines. I think that, while 
restructuring the build system, those lines have been copied to the wrong 
location. I copied them around the "FLAGS_SETUP_CFLAGS_CPU_DEP" call for 
the BUILD_CC, in order to make configure not use the target CFLAGS while 
discovering possible CFLAGS for the BUILD_CC, which was happening in our 
case.

I am also not sure if the variable BUILD_CC_DISABLE_WARNING_PREFIX is 
actually used anywhere. I could not find any user and it might be possible 
to simply remove it.

I tried the change and compiled on an amd64 linux machine for amd64, and 
cross-compiled for linux on armv7 and linux on aarch64. I don't have 
access to other cross-compilation environments and would like to ask 
others to review and try out the change.

Thanks,
Christoph