tools: bpftool: move "__printf()" attributes to header file

Some functions in bpftool have a "__printf()" format attributes to tell
the compiler they should expect printf()-like arguments. But because
these attributes are not used for the function prototypes in the header
files, the compiler does not run the checks everywhere the functions are
used, and some mistakes on format string and corresponding arguments
slipped in over time.

Let's move the __printf() attributes to the correct places.

Note: We add guards around the definition of GCC_VERSION in
tools/include/linux/compiler-gcc.h to prevent a conflict in jit_disasm.c
on GCC_VERSION from headers pulled via libbfd.

Fixes: c101189bc9 ("tools: bpftool: fix -Wmissing declaration warnings")
Reported-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/common.c

@@ -29,7 +29,7 @@
 #define BPF_FS_MAGIC		0xcafe4a11
 #endif
 
-void __printf(1, 2) p_err(const char *fmt, ...)
+void p_err(const char *fmt, ...)
 {
 	va_list ap;
 
@@ -47,7 +47,7 @@ void __printf(1, 2) p_err(const char *fmt, ...)
 	va_end(ap);
 }
 
-void __printf(1, 2) p_info(const char *fmt, ...)
+void p_info(const char *fmt, ...)
 {
 	va_list ap;