[TextAPI] Fix memory leak in SymbolSet. (#150589)

The SymbolSet class bump-ptr-allocates Symbol objects, but Symbol has a
non-trivial destructor (since Symbol's Targets member is a SmallVector):
we need to explicitly destroy the Symbol objects to ensure that no
memory is leaked.

rdar://154778728

llvm/include/llvm/TextAPI/SymbolSet.h

@@ -92,6 +92,7 @@ private:
 
 public:
   SymbolSet() = default;
+  ~SymbolSet();
   LLVM_ABI Symbol *addGlobal(EncodeKind Kind, StringRef Name, SymbolFlags Flags,
                              const Target &Targ);
   size_t size() const { return Symbols.size(); }

llvm/lib/TextAPI/SymbolSet.cpp

@@ -11,6 +11,11 @@
 using namespace llvm;
 using namespace llvm::MachO;
 
+SymbolSet::~SymbolSet() {
+  for (auto &[Key, Sym] : Symbols)
+    Sym->~Symbol();
+}
+
 Symbol *SymbolSet::addGlobalImpl(EncodeKind Kind, StringRef Name,
                                  SymbolFlags Flags) {
   Name = copyString(Name);

llvm/test/tools/llvm-readtapi/many-targets.test

@@ -0,0 +1,20 @@
+; RUN: rm -rf %t
+; RUN: split-file %s %t
+;
+; RUN: llvm-readtapi %t/many-targets.tbd
+;
+; Check that tbds containing symbols with many targets parse correctly (and in
+; particular parse without leaks).
+
+;--- many-targets.tbd
+--- !tapi-tbd
+tbd-version:     4
+targets:         [ x86_64-macos, x86_64-maccatalyst, arm64-macos, arm64-maccatalyst,
+                   arm64e-macos, arm64e-maccatalyst, arm64-ios, arm64e-ios ]
+install-name:    '/usr/lib/foo.dylib'
+current-version: 1
+exports:
+  - targets:         [ x86_64-macos, x86_64-maccatalyst, arm64-macos, arm64-maccatalyst,
+                       arm64e-macos, arm64e-maccatalyst, arm64-ios, arm64e-ios ]
+    symbols:         [ 'foo' ]
+...