[PATCH 3/3] Makefile: use -Wdeclaration-after-statement if supported

[Adam Spiers <git@adamspiers.org>]

CodingGuidelines requests that code should be nice to older C compilers.
Since modern gcc can warn on code written using newer dialects such as C99,
it makes sense to take advantage of this by auto-detecting this capability
and enabling it when found.

Signed-off-by: Adam Spiers <git@adamspiers.org>
---
If we adopt this approach, it may make sense to enable other flags
where available (e.g. -Wzero-as-null-pointer-constant, maybe even
-ansi).  In that case, something like this might be a more efficient
way of writing it:

    GCC_FLAGS=-Wdeclaration-after-statement,-Wanother-flag,-Wand-another
    GCC_FLAGS_REGEXP=$(shell echo $(GCC_FLAGS) | sed 's/,/\\|/g')
    GCC_SUPPORTED_FLAGS=$(shell cc --help -v 2>&1 | \
            sed -n '/.* \($(GCC_FLAGS_REGEXP)\) .*/{s//\1/;p}')

 Makefile | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index a49d1db..aae70d4 100644
--- a/Makefile
+++ b/Makefile
@@ -331,8 +331,13 @@ endif
 # CFLAGS and LDFLAGS are for the users to override from the command line.
 
 CFLAGS = -g -O2 -Wall
+GCC_DECL_AFTER_STATEMENT = \
+	$(shell $(CC) --help -v 2>&1 | \
+		grep -q -- -Wdeclaration-after-statement && \
+	  echo -Wdeclaration-after-statement)
+GCC_FLAGS = $(GCC_DECL_AFTER_STATEMENT)
+ALL_CFLAGS = $(CPPFLAGS) $(CFLAGS) $(GCC_FLAGS)
 LDFLAGS =
-ALL_CFLAGS = $(CPPFLAGS) $(CFLAGS)
 ALL_LDFLAGS = $(LDFLAGS)
 STRIP ?= strip
 
-- 
1.7.12.1.396.g53b3ea9