Reapply "[lld] Support thumb PLTs" (#93631) (#93644)

This reverts commit 7832769d32.

This was reverted prior due to a test failure on the windows builder. I
think this was because we didn't specify the triple and assumed windows.
The other tests use the full triple specifying linux, so we follow suite
here.

---

We are using PLTs for cortex-m33 which only supports thumb. More
specifically, this is for a very restricted use case. There's no MMU so
there's no sharing of virtual addresses between two processes, but this
is fine. The MCU is used for running [chre
nanoapps](https://android.googlesource.com/platform/system/chre/+/HEAD/doc/nanoapp_overview.md)
for android. Each nanoapp is a shared library (but effectively acts as
an executable containing a test suite) that is loaded and run on the MCU
one binary at a time and there's only one process running at a time, so
we ensure that the same text segment cannot be shared by two different
running executables. GNU LD supports thumb PLTs but we want to migrate
to a clang toolchain and use LLD, so thumb PLTs are needed.

lld/ELF/InputFiles.cpp

@@ -194,6 +194,18 @@ static void updateSupportedARMFeatures(const ARMAttributeParser &attributes) {
   if (arch >= ARMBuildAttrs::CPUArch::v8_M_Base &&
       profile == ARMBuildAttrs::MicroControllerProfile)
     config->armCMSESupport = true;
+
+  // The thumb PLT entries require Thumb2 which can be used on multiple archs.
+  // For now, let's limit it to ones where ARM isn't available and we know have
+  // Thumb2.
+  std::optional<unsigned> armISA =
+      attributes.getAttributeValue(ARMBuildAttrs::ARM_ISA_use);
+  std::optional<unsigned> thumb =
+      attributes.getAttributeValue(ARMBuildAttrs::THUMB_ISA_use);
+  bool noArmISA = !armISA || *armISA == ARMBuildAttrs::Not_Allowed;
+  bool hasThumb2 = thumb && *thumb >= ARMBuildAttrs::AllowThumb32;
+  if (noArmISA && hasThumb2)
+    config->armThumbPLTs = true;
 }
 
 InputFile::InputFile(Kind k, MemoryBufferRef m)