Like in r12-7519-g027e30414492d50feb2854aff38227b14300dc4b, I've done
git grep -v 'long long\|optab optab\|template template\|double double' | grep ' \([a-zA-Z]\+\) \1 '

This is just part of the changes, mostly for non-gcc directories.
I'll try to get to the rest soon.  Obviously, the above command also
finds cases which are correct as is and shouldn't be changed, so one
needs to manually inspect everything.

I'd hope most of it is pretty obvious, but the config/ and libstdc++-v3/
hunks include a tweak in a license wording, though other copies of the
similar license have the wording right.

2024-04-02  Jakub Jelinek  <jakub@redhat.com>

	* Makefile.tpl: Fix duplicated words; returns returns ->
	returns.
config/
	* lcmessage.m4: Fix duplicated words; can can -> can,
	package package -> package.
libdecnumber/
	* decCommon.c (decFinalize): Fix duplicated words in
	comment; the the -> the.
libgcc/
	* unwind-dw2-fde.c (struct fde_accumulator): Fix duplicated
	words in comment; is is -> is.
libgfortran/
	* configure.host: Fix duplicated words; the the -> the.
libgm2/
	* configure.host: Fix duplicated words; the the -> the.
libgomp/
	* libgomp.texi (OpenMP 5.2): Fix duplicated words; with with ->
	with.
	(omp_target_associate_ptr): Fix duplicated words; either either ->
	either.
	(omp_init_allocator): Fix duplicated words; be be -> be.
	(omp_realloc): Fix duplicated words; is is -> is.
	(OMP_ALLOCATOR): Fix duplicated words; other other -> other.
	* priority_queue.h (priority_queue_multi_p): Fix duplicated words;
	to to -> to.
libiberty/
	* regex.c (byte_re_match_2_internal): Fix duplicated words in comment;
	next next -> next.
	* dyn-string.c (dyn_string_init): Fix duplicated words in comment;
	of of -> of.
libitm/
	* beginend.cc (GTM::gtm_thread::begin_transaction): Fix duplicated
	words in comment; not not -> not to.
libobjc/
	* init.c (duplicate_classes): Fix duplicated words in comment; in in
	-> in.
	* sendmsg.c (__objc_prepare_dtable_for_class): Fix duplicated words
	in comment; the the -> the.
	* encoding.c (objc_layout_structure): Likewise.
libstdc++-v3/
	* acinclude.m4: Fix duplicated words; file file -> file can.
	* configure.host: Fix duplicated words; the the -> the.
libvtv/
	* vtv_rts.cc (vtv_fail): Fix duplicated words; to to -> to.
	* vtv_fail.cc (vtv_fail): Likewise.