[Driver] Don't pass ELF shared objects to swift-autolink-extract

Prior to performing linking on ELF platforms (except the PS4) we extract
autolink information from the object files that will be used during linking.
The current implementation passes all the linker inputs that are marked as an
TY_Object to swift-autolink-extract. There are a two cases where this is
not necessary or problematic.

In the first case, we are looking at an ELF shared object. Although
harmless, this is wasted work. Specifically, the `.swift1_autolink_entries`
entry in the object files are marked as `SHF_EXCLUDE`, meaning they will not be
merged into the final product during linking.

In the second case, we are linking against a linker script that looks like an
ELF shared object (ends with `.so`). In the previous case, the autolink-extract
step will succeed even if it does unnecessary work. In this case, the
autolink-extract step will fail because it cannot recognize the linker script as
an object file. You will observe an error something like this:
```
<unknown>:0: error: error opening input file '/path/to/libLinkerScript.so'
(The file was not recognized as a valid object file
```
Although your linker will know what to do with it, autolink-extract will halt
before you get to that point.

Author: bulbazord

lib/Driver/Driver.cpp

@@ -2107,11 +2107,21 @@ void Driver::buildActions(SmallVectorImpl<const Action *> &TopLevelActions,
     // On ELF platforms there's no built in autolinking mechanism, so we
     // pull the info we need from the .o files directly and pass them as an
     // argument input file to the linker.
+    const auto &Triple = TC.getTriple();
     SmallVector<const Action *, 2> AutolinkExtractInputs;
     for (const Action *A : AllLinkerInputs)
-      if (A->getType() == file_types::TY_Object)
+      if (A->getType() == file_types::TY_Object) {
+        // Shared objects on ELF platforms don't have a swift1_autolink_entries
+        // section in them because the section in the .o files is marked as
+        // SHF_EXCLUDE.
+        if (auto *IA = dyn_cast<InputAction>(A)) {
+          StringRef ObjectName = IA->getInputArg().getValue();
+          if (Triple.getObjectFormat() == llvm::Triple::ELF &&
+              ObjectName.endswith(".so"))
+            continue;
+        }
         AutolinkExtractInputs.push_back(A);
-    const auto &Triple = TC.getTriple();
+      }
     const bool AutolinkExtractRequired =
         (Triple.getObjectFormat() == llvm::Triple::ELF && !Triple.isPS4()) ||
         Triple.getObjectFormat() == llvm::Triple::Wasm ||

test/Driver/Inputs/libEmpty.so

@@ -0,0 +1 @@
+/* Just an empty file that looks like an ELF shared object */

test/Driver/autolink-no-shared-objects-elf.swift

@@ -0,0 +1,5 @@
+// RUN: %target-swiftc_driver -### %s %S/Inputs/libEmpty.so | %FileCheck %s
+
+// REQUIRES: autolink-extract
+
+// CHECK-NOT: swift-autolink-extract {{.+}}.o {{.+}}Inputs/libEmpty.so -o {{.+}}.autolink