!compiler: drop CONFIG_HAVE_LONG_LONG and require long long support

Every compiler supported by NuttX provides the "long long" types,
so the CONFIG_HAVE_LONG_LONG indirection is no longer useful.
Remove the option from include/nuttx/compiler.h and treat
"long long" as unconditionally available across the OS.

In addition to deleting the guard itself, this commit unconditionally
enables the long-long flavored helpers that used to be gated behind
it:

  - libs/libc/fixedmath: drop the soft-emulated b32/ub32 routines
    in lib_fixedmath.c (-261 lines) and trim the matching
    prototypes, Make.defs and CMakeLists.txt entries; keep only
    the long-long backed implementations.
  - include/sys/endian.h, include/strings.h, libs/libc/string
    /lib_ffsll.c, lib_flsll.c: always expose the 64-bit byte-swap
    and ffsll/flsll variants.
  - libs/libm/libm/lib_llround{,f,l}.c: drop the empty stubs.
  - libs/libc/stdlib (atoll, llabs, lldiv, strtoll/ull, rand48,
    strtold), libs/libc/stream (libvsprintf, libvscanf,
    libbsprintf, ultoa_invert), libs/libc/misc (crc64, crc64emac),
    libs/libc/inttypes/strtoimax, libs/libc/lzf, libs/libc/libc.csv,
    libs/libc/string (memset, vikmemcpy): remove the
    #ifdef CONFIG_HAVE_LONG_LONG branches.
  - include/{stddef.h,stdlib.h,fixedmath.h,sys/epoll.h,cxx/cstdlib,
    nuttx/audio/audio.h,nuttx/crc64.h,nuttx/lib/math.h,
    nuttx/lib/math32.h,nuttx/lib/stdbit.h}: same guard cleanup.
  - drivers/note/note_driver.c, fs/spiffs/src/spiffs.h,
    sched/irq/irq_procfs.c: drop their local guards as well.
  - Documentation/applications/netutils/ntpclient/index.rst:
    refresh the documentation snippet.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

libs/libc/fixedmath/CMakeLists.txt

@@ -20,5 +20,4 @@
 #
 # ##############################################################################
 
-target_sources(c PRIVATE lib_fixedmath.c lib_b16sin.c lib_b16cos.c
-                         lib_b16atan2.c lib_ubsqrt.c)
+target_sources(c PRIVATE lib_b16sin.c lib_b16cos.c lib_b16atan2.c lib_ubsqrt.c)