CI ARM: set CFLAGS for 32-bit off_t

The flags queried also for 64-bit ARM but it is empty there.

This does basically the same as the commit f46a101, that adds
_FILE_OFFSET_BITS=64 define to config.h. But the config.h may not be
always included now.

+ compat/misc: typo in comment + assert 64b off_t (off_t should be
actually 64b in _OFF64 env and >= 64b in _OFFBIG so assert at least 64)

Author: MartinPulec

.github/scripts/Linux/arm/build.sh

@@ -10,6 +10,16 @@ export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:${PKG_CONFIG_PATH:+":$PKG_CONFIG
 ARCH=$(dpkg --print-architecture)
 APPNAME=UltraGrid-latest-${ARCH}.AppImage
 
+# set 64-bit off_t for 32-bit ARM, see the following (POSIX 2024 will use V8):
+# <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html>
+# TODO: this is duplicite of AC_SYS_LARGEFILE - figure out how to keep
+# that without needing to include the config.h in headers
+CENV=$(getconf POSIX_V7_WIDTH_RESTRICTED_ENVS | grep -E 'OFFBIG|OFF64' |
+  head -n 1)
+CFLAGS=${CFLAGS:+$CFLAGS }$(getconf "${CENV}_CFLAGS")
+CXXFLAGS=${CXXFLAGS:+$CXXFLAGS }$(getconf "${CENV}_CFLAGS")
+export CFLAGS CXXFLAGS
+
 # shellcheck disable=SC2086 # intentional
 set -- $FEATURES
 set -- "$@" --enable-drm_disp

src/compat/misc.h

@@ -57,9 +57,9 @@
                 #define fseeko _fseeki64
         #else
                 #ifndef __cplusplus
-                        #include <assert.h> // static_assert macro (until c32)
+                        #include <assert.h> // static_assert macro (until C23)
                 #endif
-                static_assert(sizeof(off_t) > 4, "32b off_t");
+                static_assert(sizeof(off_t) >= 8, "off_t less than 64b");
         #endif // !defined _WIN32
 #endif // defined WANT_FSEEKO