[MC][AArch64][ARM][X86] Push target-dependent assembler flags into targets (#139844)

The .syntax unified directive and .codeX/.code X directives are, other
than some simple common printing code, exclusively implemented in the
targets themselves. Thus, remove the corresponding MCAF_* flags and
reimplement the directives solely within the targets. This avoids
exposing all targets to all other targets' flags.

Since MCAF_SubsectionsViaSymbols is all that remains, convert it to its
own function like other directives, simplifying its implementation.

Note that, on X86, we now always need a target streamer when parsing
assembly, as it's now used for directives that aren't COFF-specific. It
still does not however need to do anything when producing a non-COFF
object file, so this commit does not introduce any new target streamers.

There is some churn in test output, and corresponding UTC regex changes,
due to comments no longer being flushed by these various directives (and
EmitEOL is not exposed outside MCAsmStreamer.cpp so we couldn't do so
even if we wanted to), but that was a bit odd to be doing anyway.

This is motivated by Morello LLVM, which adds yet another assembler flag
to distinguish A64 and C64 instruction sets, but did not update every
switch and so emits warnings during the build. Rather than fix those
warnings it seems better to instead make the problem not exist in the
first place via this change.

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index a196842..618a35b 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -1245,7 +1245,10 @@ void MCStreamer::emitAbsoluteSymbolDiffAsULEB128(const MCSymbol *Hi,
   emitULEB128Value(Diff);
 }
 
-void MCStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {}
+void MCStreamer::emitSubsectionsViaSymbols() {
+  llvm_unreachable(
+      "emitSubsectionsViaSymbols only supported on Mach-O targets");
+}
 void MCStreamer::emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {}
 void MCStreamer::beginCOFFSymbolDef(const MCSymbol *Symbol) {
   llvm_unreachable("this directive only supported on COFF targets");