PowerPC: Do not use llc -march in tests.

`llc -march` is problematic because it only switches the target
architecture, but leaves the operating system unchanged. This
occasionally leads to indeterministic tests because the OS from
LLVM_DEFAULT_TARGET_TRIPLE is used.

However we can simply always use `llc -mtriple` instead. This changes
all the tests to do this to avoid people using -march when they copy and
paste parts of tests.

This patch:
- Removes -march if the .ll file already has a matching `target triple`
  directive or -mtriple argument.
- In all other cases changes -march=ppc32/-march=ppc64 to
  -mtriple=ppc32--/-mtriple=ppc64--

See also the discussion in https://reviews.llvm.org/D35287

llvm-svn: 309754
diff --git a/llvm/test/CodeGen/PowerPC/tls-cse.ll b/llvm/test/CodeGen/PowerPC/tls-cse.ll
index 6529469..c770209 100644
--- a/llvm/test/CodeGen/PowerPC/tls-cse.ll
+++ b/llvm/test/CodeGen/PowerPC/tls-cse.ll
@@ -1,5 +1,5 @@
-; RUN: llc -verify-machineinstrs -march=ppc64 -mcpu=pwr7 -O2 -relocation-model=pic < %s | FileCheck %s
-; RUN: llc -verify-machineinstrs -march=ppc64 -mcpu=pwr7 -O2 -relocation-model=pic < %s | grep "__tls_get_addr" | count 1
+; RUN: llc -verify-machineinstrs -mcpu=pwr7 -O2 -relocation-model=pic < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mcpu=pwr7 -O2 -relocation-model=pic < %s | grep "__tls_get_addr" | count 1
 
 ; This test was derived from LLVM's own
 ; PrettyStackTraceEntry::~PrettyStackTraceEntry().  It demonstrates an