A general best practice for SPDX is that Makefiles should have an
identifier, add these as everything else is currently covered.
Signed-off-by: NTom Rini <trini@konsulko.com>

These lines originate in Linux;  it looks like Linux folks chose to
hide bunch of warnings reported by clang rather than fixing C code.

In U-boot, warnings are being fixed thanks to Jeroen's great efforts.
Let's stop suppressing clang warnings.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jeroen Hofstee <jeroen@myspectrum.nl>

This commit was imported from Linux Kernel:
commit a86fe353 written by me.

W=... provides extra gcc checks.

Having such code in scripts/Makefile.build results in the same flags
being added to KBUILD_CFLAGS multiple times becuase
scripts/Makefile.build is invoked every time Kbuild descends into
the subdirectories.

Since the top Makefile is already too cluttered, this commit moves
all of extra gcc check stuff to a new file scripts/Makefile.extrawarn,
which is included from the top Makefile.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>