[Hexagon,test] Change llc -march= to -mtriple=

Similar to 806761a7629df268c8aed49657aeccffa6bca449

-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the

[Hexagon,test] Change llc -march= to -mtriple=

Similar to 806761a7629df268c8aed49657aeccffa6bca449

-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense.

Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize $unknown-apple-darwin as ELF instead
of rejecting it outrightly.

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[Hexagon] Convert some tests to opaque pointers (NFC)

OpaquePtr: Bulk update tests to use typed byval

Upgrade of the IR text tests should be the only thing blocking making
typed byval mandatory. Partially done through regex and partially
manual.

Add support for Linux/Musl ABI

Differential revision: https://reviews.llvm.org/D72701

The patch adds a new option ABI for Hexagon. It primary deals with
the way variable arguments are passed and is

Add support for Linux/Musl ABI

Differential revision: https://reviews.llvm.org/D72701

The patch adds a new option ABI for Hexagon. It primary deals with
the way variable arguments are passed and is use in the Hexagon Linux Musl
environment.

If a callee function has a variable argument list, it must perform the
following operations to set up its function prologue:

1. Determine the number of registers which could have been used for passing
unnamed arguments. This can be calculated by counting the number of
registers used for passing named arguments. For example, if the callee
function is as follows:

int foo(int a, ...){ ... }

... then register R0 is used to access the argument ' a '. The registers
available for passing unnamed arguments are R1, R2, R3, R4, and R5.

2. Determine the number and size of the named arguments on the stack.

3. If the callee has named arguments on the stack, it should copy all of these
arguments to a location below the current position on the stack, and the
difference should be the size of the register-saved area plus padding
(if any is necessary).

The register-saved area constitutes all the registers that could have
been used to pass unnamed arguments. If the number of registers forming
the register-saved area is odd, it requires 4 bytes of padding; if the
number is even, no padding is required. This is done to ensure an 8-byte
alignment on the stack. For example, if the callee is as follows:

int foo(int a, ...){ ... }

... then the named arguments should be copied to the following location:

current_position - 5 (for R1-R5) * 4 (bytes) - 4 (bytes of padding)

If the callee is as follows:

int foo(int a, int b, ...){ ... }

... then the named arguments should be copied to the following location:

current_position - 4 (for R2-R5) * 4 (bytes) - 0 (bytes of padding)

4. After any named arguments have been copied, copy all the registers that
could have been used to pass unnamed arguments on the stack. If the number
of registers is odd, leave 4 bytes of padding and then start copying them
on the stack; if the number is even, no padding is required. This
constitutes the register-saved area. If padding is required, ensure
that the start location of padding is 8-byte aligned. If no padding is
required, ensure that the start location of the on-stack copy of the
first register which might have a variable argument is 8-byte aligned.

5. Decrement the stack pointer by the size of register saved area plus the
padding. For example, if the callee is as follows:

int foo(int a, ...){ ... } ;

... then the decrement value should be the following:

5 (for R1-R5) * 4 (bytes) + 4 (bytes of padding) = 24 bytes

The decrement should be performed before the allocframe instruction.
Increment the stack-pointer back by the same amount before returning
from the function.

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