[Hexagon] Fix test on OpenBSD

[brad]

Summary

The test specifies a CPU arch but not a particular OS. So if run on OpenBSD it acts as if it's an OpenBSD/hexagon system. OpenBSD uses guard_local instead of stack_chk_guard so the test will fail. So specify an OS other than OpenBSD fixes the tet.

[MaskRay]

LGTM.

llvm/test/CodeGen/Hexagon/sdata-stack-guard.ll

 ; Check that the __stack_chk_guard was placed in small data.
-; RUN: llc -march=hexagon -O2 -hexagon-small-data-threshold=4 < %s | FileCheck -check-prefix=GPREL %s
+; RUN: llc -march=hexagon -mtriple=hexagon-unknown-linux-gnu -O2 -hexagon-small-data-threshold=4 < %s | FileCheck -check-prefix=GPREL %s
 ; GPREL: memw(gp+#__stack_chk_guard)
 
 ; For threshold less than 4 (size of address), the variable is not placed in small-data
-; RUN: llc -march=hexagon -O2 -hexagon-small-data-threshold=0 < %s | FileCheck -check-prefix=ABS %s
+; RUN: llc -march=hexagon -mtriple=hexagon-unknown-linux-gnu -O2 -hexagon-small-data-threshold=0 < %s | FileCheck -check-prefix=ABS %s
 ; ABS: memw(##__stack_chk_guard)
 
 @g0 = private unnamed_addr constant [37 x i8] c"This string is longer than 16 bytes\0A\00", align 1
 @g1 = private unnamed_addr constant [15 x i8] c"\0AChar 20 = %c\0A\00", align 1
 
 ; Function Attrs: noinline nounwind ssp
 define zeroext i8 @f0(i32 %a0) #0 {
 b0: