[PATCH] libgcc/crtstuff.c: Fix incorrect alignment of entries in CRT data structures (PR target/91306)

[Jozef Lawrynowicz]

As described in PR target/91306, the alignment of entries in CRT data structures
as set in libgcc/crtstuff.c can be too large for msp430-elf.

crtstuff.c assumes the correct alignment of entries with a type of (void *) or
int32 is the "sizeof" that type.

However, for msp430-elf in the large memory model, pointer size is 4 bytes, but
they only need to be 2-byte aligned. Likewise for int32.

This is causing problems for __frame_dummy_init_array_entry, which gets 
inserted into .init_array.
It is being forced into a 4 byte alignment, which can result in a gap between
__frame_dummy_init_array_entry and the previous entry (or the start of the
table). So when the startup code comes to run through the entries
in .init_array, it interprets 2-bytes of padding 0s as part of a function
address, resulting in a function call to the incorrect location.

This issue has only recently appeared because msp430-elf was just transitioned
to use init/fini_array by default, as mandated by the mspabi.

The other CRT array entries in crtstuff.c are not used for msp430-elf, so aren't
causing problems.

As suggested in the PR, I tried changing the alignment of the array entry from
sizeof(func_ptr) to __alignof__(func_ptr), and this fixed the issue. In the
attached patch I also updated the other uses of sizeof in "aligned" attributes
to use __alignof__ instead.

I understand the alignment to sizeof(func_ptr) was originally added to fix an
issue on mips64 (r182066
https://gcc.gnu.org/ml/gcc-patches/2011-12/msg00393.html), however I do
not have access to a mips64 platform for which to bootstrap on. I tried building
a cross-compiler with the "aligned" attributes removed to see if I could
reproduce the failure, but the build completed successfully.
I built the mips64 cross-compiler with my patch applied and it
also completed successfully.

I successfully regtested the patch for msp430-elf. It fixes many execution
failures for msp430-elf/-mlarge.
I also successfully bootstrapped and regtested x86_64-pc-linux-gnu (g++ gcc
gfortran libatomic libgomp libitm libstdc++ objc).

According to the mips eabi (is this the right one?
http://www.cygwin.com/ml/binutils/2003-06/msg00436.html), pointers have 64-bit
size and alignment in 64-bit mode, so I am assuming using __alignof__ instead of
sizeof isn't going to cause problems.

Ok for trunk?
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