MINOR: build: force CC to set a return code when probing options

gcc returns non zero code if an option is not supported (tested
from 6.5 to 10.2).

  $ gcc -Wfoobar -E -xc - -o /dev/null < /dev/null > /dev/null 2>&1 ; echo $?
  1

clang always return 0 if an option in not recognized unless
-Werror is also passed, preventing a correct probing of options
supported by the compiler (tested with clang 6.0.1 to 11.1.0).

  $ clang -Wfoobar -E -xc - -o /dev/null < /dev/null > /dev/null 2>&1 ; echo $?
  0
  $ clang -Werror -Wfoobar -E -xc - -o /dev/null < /dev/null > /dev/null 2>&1 ; echo $?
  1

Please note today this is not visible since clang 11 exit with SIGABRT
or with return code 1 on older version due to bad file descriptor from
file descriptor handling

  $ clang -Wfoobar -E -xc - -o /dev/null < /dev/null 2>&0 ; echo $?
  Aborted (core dumped)
  134
  $ clang -Wfoobar -E -xc - -o /dev/null < /dev/null ; echo $?
  warning: unknown warning option '-Wfoobar'; did you mean '-Wformat'? [-Wunknown-warning-option]
  1 warning generated.
  0
  $ clang-11 -Werror -Wfoobar -E -xc - -o /dev/null < /dev/null ; echo $?
  error: unknown warning option '-Wfoobar'; did you mean '-Wformat'? [-Werror,-Wunknown-warning-option]
  1

This specific issue is being tracked with clang upstream in https://bugs.llvm.org/show_bug.cgi?id=49463

diff --git a/Makefile b/Makefile
index 77960ba4cac5ea15127695c5a7f9954aab8d334a..0867047fdc699ed2e43f3f36c72b1710fe186e1a 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -126,16 +126,16 @@ endif
 # Usage: CFLAGS += $(call cc-opt,option). Eg: $(call cc-opt,-fwrapv)
 # Note: ensure the referencing variable is assigned using ":=" and not "=" to
 #       call it only once.
-cc-opt = $(shell set -e; if $(CC) $(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; fi;)
+cc-opt = $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; fi;)
 
 # same but emits $2 if $1 is not supported
-cc-opt-alt = $(shell set -e; if $(CC) $(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; else echo "$(2)"; fi;)
+cc-opt-alt = $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; else echo "$(2)"; fi;)
 
 # Disable a warning when supported by the compiler. Don't put spaces around the
 # warning! And don't use cc-opt which doesn't always report an error until
 # another one is also returned.
 # Usage: CFLAGS += $(call cc-nowarn,warning). Eg: $(call cc-opt,format-truncation)
-cc-nowarn = $(shell set -e; if $(CC) -W$(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "-Wno-$(1)"; fi;)
+cc-nowarn = $(shell set -e; if $(CC) -Werror -W$(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "-Wno-$(1)"; fi;)
 
 #### Installation options.
 DESTDIR =