build: check format strings, which nothing ever did (#44)

The segfault in issue #5 was a format string: `%I64d` is MSVC-only,
glibc parses it as the GNU `I` flag with a width of 64 and an `int`
conversion, the vararg run desynchronises, and the following `%s`
dereferences an integer. It killed the node mid-sync at the first
block carrying a real transaction, deterministically.

GCC can catch this. It never got the chance, for two reasons that
had to be fixed together:

  - `-w` sat in both makefiles and suppressed every diagnostic. It
    cannot be narrowed; it wins over any -W or -Werror= that follows,
    so it had to go. The four -Wno- entries replacing it are the
    categories this 2009-era tree actually produces (measured: 248
    deprecated-declarations, 157 write-strings, 18 narrowing, 1
    unused-result), silenced by name instead of wholesale.

  - Even with -Wformat on, nothing was checked. GCC only inspects
    format strings for functions it knows are printf-like, and every
    format string here goes through strprintf, error, my_snprintf, or
    OutputDebugStringF -- `printf` itself is #defined to the last of
    those. None carried a format attribute, so the entire tree was
    invisible to the check. They are annotated now.

Annotating surfaced 77 warnings across 17 distinct sites, all fixed
here. Most were size_t or int64 passed to %d, harmless on x86-64 but
wrong. Two were not cosmetic:

  - CBlockIndex::ToString printed pprev/pnext with %08x, truncating
    both pointers to 32 bits, so the two fields that line exists to
    show were unreliable on every 64-bit build.

  - CInv::GetCommand threw "type=% unknown type", where the % ate the
    space as a flag and the u as its conversion. The message read
    "type= 3nknown type".

PRId64 is now one spelling for every target. Its MSVCRT branch was
what produced "I64d" in the first place, it is pointless against UCRT
which takes the C99 forms, the rest of the tree already prints int64
with %lld on Windows, and its only user (i64tostr) is dead code.
Collapsing it lets both builds share the gnu_printf archetype --
ms_printf would reject %zu, which this tree uses and UCRT supports,
while waving through the %I64d that crashes.

Verified on both platforms: clean build, and reintroducing the
issue #5 specifier now fails compilation rather than shipping.

  main.h:410:50: error: unknown conversion type character 'I' in format
  main.h:410:70: error: format '%s' expects argument of type 'char*',
                        but argument 3 has type 'long long int'

That second line is the crash itself, caught at build time.

Runtime checked on both: node syncs past the block from issue #5, and
the repaired log lines read correctly --

  before:  CTxOut(nValue=          50.%08I64d, scriptPubKey=(null))
  after:   CTxOut(nValue=50.00000000, scriptPubKey=0xE1C7EF3E706002)

Four '_WIN32_WINNT redefined' warnings remain on Windows. Silencing
them means letting a system header pick the Windows API level instead
of this tree, which is a separate decision from format checking.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/net.h b/src/net.h
index d13de61..364fbfb 100644
--- a/src/net.h
+++ b/src/net.h
@@ -392,7 +392,9 @@ public:
     const char* GetCommand() const
     {
         if (!IsKnownType())
-            throw std::out_of_range(strprintf("CInv::GetCommand() : type=% unknown type", type));
+            // Was "type=% unknown type": the % swallowed the space as a flag and
+            // the u as the conversion, so this read "type= 3nknown type".
+            throw std::out_of_range(strprintf("CInv::GetCommand() : type=%d unknown type", type));
         return ppszTypeName[type];
     }