[PATCH] Fix passing/returning of complex data for PowerPC 32-bit

[Luis Machado]

The PowerPC 32-bit unified ABI states that there are two ways of passing 
and returning complex type data:

- Pointer, in a register, to a memory area.
- Data in registers.

The problem is that it is not clear how to detect which variation a 
program is using. GDB currently does a bit of both. It uses the first 
mechanism for passing parameters and uses both to return data, depending 
on the size of the data type. It is a bit messy because GDB is not 
handling complex types explicitly.

Checking the gdb.base/callfuncs.exp testcase for a PowerPC 32-bit 
target, with code built with GCC, showed a few failures related to 
complex types.

This patch steers GDB towards what GCC seems to generate for PowerPC 
32-bit and handles complex type passing/return via general registers 
(the second option). All failures are gone.

The problem here is if some other target/compiler is using the other 
variation. So, for those that have a PowerPC 32-bit handy, can you 
confirm it works reliably? I'm thinking AIX, Darwin or some other eabi 
target.

Otherwise, does this look reasonable?

Regards,
Luis
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