[PATCH v2 1/4] build: make cc-option properly deal with unrecognized sub-options

[Jan Beulich <jbeulich@xxxxxxxx>]

In options like -march=, it may be only the sub-option which is
unrecognized by the compiler. In such an event the error message often
splits option and argument, typically saying something like "bad value
'<argument>' for '<option>'. Extend the grep invocation accordingly,
also accounting for Clang to not mention e.g. -march at all when an
incorrect argument was given for it.

To keep things halfway readable, re-wrap and re-indent the entire
construct.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
In principle -e "$$pat" could now be omitted from the grep invocation,
since if that matches, both $$opt and $$arg will, too. But I thought I'd
leave it for completeness.
---
v2: Further relax grep patterns for clang, which doesn't mention -march
    when complaining about an invalid argument to it.

--- a/Config.mk
+++ b/Config.mk
@@ -90,9 +90,14 @@ PYTHON_PREFIX_ARG ?= --prefix="$(prefix)
 # of which would indicate an "unrecognized command-line option" warning/error.
 #
 # Usage: cflags-y += $(call cc-option,$(CC),-march=winchip-c6,-march=i586)
-cc-option = $(shell if test -z "`echo 'void*p=1;' | \
-              $(1) $(2) -c -o /dev/null -x c - 2>&1 | grep -- 
$(2:-Wa$(comma)%=%) -`"; \
-              then echo "$(2)"; else echo "$(3)"; fi ;)
+cc-option = $(shell pat='$(2:-Wa$(comma)%=%)'; \
+                    opt="$${pat%%=*}" arg="$${pat\#*=}"; \
+                    if test -z "`echo 'void*p=1;' | \
+                                 $(1) $(2) -c -o /dev/null -x c - 2>&1 | \
+                                 grep -e "$$pat" -e "$$opt" -e "$$arg" -`"; \
+                    then echo "$(2)"; \
+                    else echo "$(3)"; \
+                    fi;)
 
 # cc-option-add: Add an option to compilation flags, but only if supported.
 # Usage: $(call cc-option-add CFLAGS,CC,-march=winchip-c6)