build system: remove KBUILD_STR()

When using GNU Make >=4.3, the KBUILD_STR() definition interferes badly
with dependency checks during build, and forces a complete rebuild every
time Make runs.

In if_changed_rule, Kconfig checks if the command used to build a file
has changed since last execution. The previous command is stored in the
generated .<file>.o.cmd file. For example applets/.applets.o.cmd defines
a "cmd_applets/applets.o" variable:

	cmd_applets/applets.o := gcc ... -D"KBUILD_STR(s)=#s" ...

Here the '#' should be escaped with a backslash, otherwise GNU Make
interprets it as starting a comment, and ignore the rest of the
variable. As a result of this truncation, the previous command doesn't
equal the new command and Make rebuilds each target.

The problem started to appear when GNU Make 4.3 (released January 2020),
introduced a backward-incompatible fix to macros containing a '#'. While
the above use of '#', a simple Make variable, still needs to be escaped,
a '#' within a function invocation doesn't need to be escaped anymore.
As Martin Dorey explained on the GNU Make discussion [1], the above
declaration is generated from make-cmd, defined as:

	make-cmd = $(subst \#,\\\#,$(subst $$,$$$$,$(call escsq,$(cmd_$(1))))

Since GNU Make 4.3, the first argument of subst should not have a
backslash. make-cmd now looks for literally \# and doesn't find it, and
as a result doesn't add the backslash when generating .o.cmd files.

[1] http://savannah.gnu.org/bugs/?20513

We could fix it by changing make-cmd to "$(subst #,\#,...)", but to
avoid compatibility headaches, simply get rid of the KBUILD_STR
definition, as done in Linux by b42841b7bb62 ("kbuild: Get rid of
KBUILD_STR"). Quote the string arguments directly rather than asking the
preprocessor to quote them.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

scripts/trylink

@@ -50,9 +50,6 @@ check_cc() {
     echo "int main(int argc,char**argv){return argv?argc:0;}" >"$tempname".c
     # Can use "-o /dev/null", but older gcc tend to *unlink it* on failure! :(
     # Was using "-xc /dev/null", but we need a valid C program.
-    # "eval" may be needed if CFLAGS can contain
-    # '... -D"BB_VER=KBUILD_STR(1.N.M)" ...'
-    # and we need shell to process quotes!
     $CC $CFLAGS $LDFLAGS $1 "$tempname".c -o "$tempname" >/dev/null 2>&1
     exitcode=$?
     rm -f "$tempname" "$tempname".c "$tempname".o