minimal gcc version for jdk/jdk and usage of -Wno-int-in-bool-context flag in HS build

[Baesken, Matthias]

Hello,  I noticed  that  we currently set  flags for gcc  to disable warnings.

See

https://hg.openjdk.java.net/jdk/jdk/file/896e80158d35/make/hotspot/lib/CompileJvm.gmk

DISABLED_WARNINGS_gcc := extra parentheses comment unknown-pragmas address \
    delete-non-virtual-dtor char-subscripts array-bounds int-in-bool-context \
    ignored-qualifiers  missing-field-initializers implicit-fallthrough \
    empty-body strict-overflow sequence-point maybe-uninitialized \
    misleading-indentation


However   int-in-bool-context   (  -Wnoint-in-bool-context  )   seems to be available only  in gcc 7 + .
Example call  with gcc  6  leads to a warning  :

/gcc-6/bin/gcc         sizeof.c  -Wall -Wextra   -Wno-int-in-bool-context   -o  sizeof

sizeof.c: At top level:
cc1: warning: unrecognized command line option '-Wno-int-in-bool-context'



Should  we  force all  users to gcc 7 and higher  (otherwise we could maybe check   CC_VERSION_NUMBER   in the makefile)  ?
Before  we  internally switched  our OpenJDK builds   from gcc 4.8   to gcc 7   we  had a patch  in our  build-queue  that disabled  the   -Wnoint-in-bool-context   .


Best regards, Matthias