varasm: Ensure each variable in mergeable section is the entity size [PR121394]

Now there are mergeable sections which have an entity size, we can place
decls (constants) that are smaller in size in these sections.
An example is an `long double` which has a size of 12 bytes on i686 and is
placed in the 16 bytes shareable section.

For an example with the following C++ code:
```
std::initializer_list<long double> a = {0.3l};
```

We place the constant array in the .rodata.cst16 section but we don't add a padding to 16 bytes.
```
        .section        .rodata.cst16,"aM",@progbits,16
        .align 16
        .type   _ZGR1a_, @object
        .size   _ZGR1a_, 12
_ZGR1a_:
        .long   -1717986918
        .long   -1717986919
        .long   16381
        .text
```
GAS has a workaround added to do the padding but other assemblers don't.
The gas workaround was added with https://sourceware.org/legacy-ml/binutils/2002-11/msg00615.html .
Now for the constant pool, GCC does emit a `.align` to padd out the size correctly.
This was done in r0-46282-gf41115930523b3.
The same padding should be done when emitting a variable contents when in a mergeable section.

This patch implements the padding and we now get an addition `.zero 4` which pads out the section.

Bootstrapped and tested on x86_64-linux-gnu.

	PR middle-end/121394
gcc/ChangeLog:

	* varasm.cc (assemble_variable_contents): Pad out
	mergeable sections if needed.
	(output_constant_pool_1): Change the padding to be explicit
	zeroing for mergeable sections.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

0 files changed, 0 insertions, 0 deletions