fix: CWE-134 format string audit and compiler hardening

Security:
Fix CWE-134 in iq.c: user-controlled string passed as format argument
Add G_GNUC_PRINTF annotations to all variadic printf-like wrappers
in ui.h, log.h and http_common.h
Compiler flags (configure.ac):

Replace basic -Wformat/-Wformat-nonliteral with -Wformat=2
Add -Wextra, -Wnull-dereference, -Wpointer-arith,
-Wimplicit-function-declaration, -Wundef, -Wfloat-equal,
-Wredundant-decls, -Walloc-zero
Add -fstack-protector-strong, -fno-common, -D_FORTIFY_SOURCE=2
Add GCC-specific flags via AC_COMPILE_IFELSE: -Wlogical-op,
-Wduplicated-cond, -Wduplicated-branches, -Wstringop-overflow,
-Warray-bounds=2
Suppress noisy -Wextra sub-warnings: -Wno-unused-parameter,
-Wno-missing-field-initializers, -Wno-sign-compare,
-Wno-cast-function-type
Remove AM_CFLAGS/CFLAGS duplication
Bug fixes found by new warnings:

chatlog.c: non-MUCPM redact path passed resourcepart instead of NULL
rosterwin.c: merge duplicated if/else branches into single condition
omemo.c: redundant else-if in omemo_automatic_start; remove
unnecessary scope block and goto, use early return
console.c: pointer compared to integer 0 instead of NULL
stanza.c: increase pri_str/idle_str buffers from 10 to 12 bytes
(INT_MIN = -2147483648 needs 12 bytes including NUL)
vcard.c: NULL guard for filename before g_file_set_contents
api.c: broken log_warning() calls with extra format argument
Format mismatch fixes:

chatwin.c: Jid* → char* for %s
connection.c: %x → %lx for long flags
cmd_funcs.c: %d → %zu for size_t; cast gpointer to char* for %s
cmd_defs.c: %d → %u for g_list_length() return (guint)
iq.c: barejid → fulljid for from_jid
console.c, mucwin.c, privwin.c, account.c, omemo.c, presence.c:
gpointer → (char*) casts for %s
Const-correctness and cleanup:

database.c: const for type, query, sort variables
form.c/xmpp.h: const for form_set_value parameter
files.c: refactor to early return, eliminating NULL logfile path
muc.c/muc.h: remove meaningless top-level const on return type
common.c: const for URL string literal
Remove stale declarations: cons_show_desktop_prefs (ui.h),
connection_set_priority (connection.h),
omemo_devicelist_configure_and_request (omemo.h)
test_common.c: add currb NULL check to silence -Wnull-dereference
Tooling (check-cwe134.sh):

Reduce from 5 checks to 2 (checks 1-3 redundant with -Wformat=2)
Check 1: verify known wrappers have G_GNUC_PRINTF attribute
Check 2: auto-detect unannotated variadic printf-like functions
Match both const char* and const gchar* in variadic patterns

Author: jabber.developer2 <jabber.developer2@jabber.space>

configure.ac

@@ -385,9 +385,41 @@ AC_CHECK_LIB([util], [forkpty], [AM_CONDITIONAL([HAVE_FORKPTY], [true]) FORKPTY_
 AC_SUBST([FORKPTY_LIB])
 
 ## Default parameters
-AM_CFLAGS="$AM_CFLAGS -Wall -Wno-deprecated-declarations -std=gnu99 -ggdb3"
+AM_CFLAGS="$AM_CFLAGS -Wall -Wextra -Wformat=2 -Wno-format-zero-length"
+AM_CFLAGS="$AM_CFLAGS -Wno-deprecated-declarations -Wno-unused-parameter -Wno-missing-field-initializers -Wno-sign-compare -Wno-cast-function-type"
+AM_CFLAGS="$AM_CFLAGS -Wnull-dereference -Wpointer-arith"
+AM_CFLAGS="$AM_CFLAGS -Wimplicit-function-declaration"
+AM_CFLAGS="$AM_CFLAGS -Wundef"
+AM_CFLAGS="$AM_CFLAGS -Wfloat-equal -Wredundant-decls"
+AM_CFLAGS="$AM_CFLAGS -fstack-protector-strong -fno-common"
+AM_CFLAGS="$AM_CFLAGS -D_FORTIFY_SOURCE=2"
+AM_CFLAGS="$AM_CFLAGS -std=gnu99 -ggdb3"
+
+# GCC-specific warnings (not supported by clang) — test each one
+saved_CFLAGS="$CFLAGS"
+for _flag in -Wlogical-op -Wduplicated-cond -Wduplicated-branches \
+             -Wstringop-overflow -Warray-bounds=2 -Walloc-zero; do
+    AC_MSG_CHECKING([whether $CC supports $_flag])
+    CFLAGS="$saved_CFLAGS $_flag -Werror"
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],
+        [AC_MSG_RESULT([yes]); AM_CFLAGS="$AM_CFLAGS $_flag"],
+        [AC_MSG_RESULT([no])])
+done
+CFLAGS="$saved_CFLAGS"
+
 AM_LDFLAGS="$AM_LDFLAGS -export-dynamic"
 
+# Linker hardening (RELRO + immediate binding)
+saved_LDFLAGS="$LDFLAGS"
+for _flag in -Wl,-z,relro -Wl,-z,now; do
+    AC_MSG_CHECKING([whether linker supports $_flag])
+    LDFLAGS="$saved_LDFLAGS $_flag"
+    AC_LINK_IFELSE([AC_LANG_PROGRAM()],
+        [AC_MSG_RESULT([yes]); AM_LDFLAGS="$AM_LDFLAGS $_flag"],
+        [AC_MSG_RESULT([no])])
+done
+LDFLAGS="$saved_LDFLAGS"
+
 AS_IF([test "x$enable_coverage" = xyes],
     [AM_CFLAGS="$AM_CFLAGS --coverage -O0"
      AM_LDFLAGS="$AM_LDFLAGS --coverage"
@@ -401,7 +433,7 @@ AS_IF([test "x$PLATFORM" = xosx],
 AM_CFLAGS="$AM_CFLAGS $PTHREAD_CFLAGS $glib_CFLAGS $gio_CFLAGS $curl_CFLAGS ${SQLITE_CFLAGS}"
 AM_CFLAGS="$AM_CFLAGS $libnotify_CFLAGS ${GTK_CFLAGS} $python_CFLAGS"
 AM_CFLAGS="$AM_CFLAGS -DTHEMES_PATH=\"\\\"$THEMES_PATH\\\"\" -DICONS_PATH=\"\\\"$ICONS_PATH\\\"\" -DGLOBAL_PYTHON_PLUGINS_PATH=\"\\\"$GLOBAL_PYTHON_PLUGINS_PATH\\\"\" -DGLOBAL_C_PLUGINS_PATH=\"\\\"$GLOBAL_C_PLUGINS_PATH\\\"\""
-AM_CFLAGS="$AM_CFLAGS $CFLAGS"
+
 LIBS="$glib_LIBS $gio_LIBS $PTHREAD_LIBS $curl_LIBS $libnotify_LIBS $python_LIBS ${GTK_LIBS} ${SQLITE_LIBS} $LIBS"
 
 AC_SUBST(AM_LDFLAGS)