[llvm] [Hexagon] Add missing patterns to select PFALSE and PTRUE (PR #138712)

[via llvm-commits]

h-vetinari wrote:

This landed in v20.1.5 via #138770, and seems to cause a test failure when building llvm: 
```
******************** TEST 'LLVM :: CodeGen/Hexagon/isel/pfalse-v4i1.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: $SRC_DIR/build/bin/llc -march=hexagon -debug-only=isel 2>&1 < $SRC_DIR/llvm/test/CodeGen/Hexagon/isel/pfalse-v4i1.ll - | $SRC_DIR/build/bin/FileCheck $SRC_DIR/llvm/test/CodeGen/Hexagon/isel/pfalse-v4i1.ll
+ $SRC_DIR/build/bin/llc -march=hexagon -debug-only=isel -
+ $SRC_DIR/build/bin/FileCheck $SRC_DIR/llvm/test/CodeGen/Hexagon/isel/pfalse-v4i1.ll
$SRC_DIR/llvm/test/CodeGen/Hexagon/isel/pfalse-v4i1.ll:3:10: error: CHECK: expected string not found in input
; CHECK: [[R0:%[0-9]+]]:intregs = A2_tfrsi 0
         ^
<stdin>:1:1: note: scanning from here
llc: Unknown command line argument '-debug-only=isel'. Try: '$SRC_DIR/build/bin/llc --help'
^
<stdin>:1:22: note: possible intended match here
llc: Unknown command line argument '-debug-only=isel'. Try: '$SRC_DIR/build/bin/llc --help'
                     ^

Input file: <stdin>
Check file: $SRC_DIR/llvm/test/CodeGen/Hexagon/isel/pfalse-v4i1.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           1: llc: Unknown command line argument '-debug-only=isel'. Try: '$SRC_DIR/build/bin/llc --help' 
check:3'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
check:3'1                          ?                                                                                                                                         possible intended match
           2: llc: Did you mean '--debug-pass=isel'? 
check:3'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>
```

https://github.com/llvm/llvm-project/pull/138712