[ifs] Fix bug where exclude only excluded when outputting ifs files

[abrachet]

Summary

Now output elf files will also have excluded symbols removed.

llvm/test/tools/llvm-ifs/exclude.test

 ## Test --exclude flag
 
 # RUN: llvm-ifs --input-format=IFS --output-ifs=- --exclude='exclude*' %s | FileCheck %s
 
+# Check that exclude excludes from elf files too.
+# RUN: llvm-ifs %s --output-elf - --exclude='exclude*' | llvm-ifs - --output-ifs - | FileCheck %s
+
 # RUN: llvm-ifs --input-format=IFS --output-ifs=- --exclude='exclude*' \
 # RUN: --strip-undefined %s | FileCheck %s --check-prefix=BOTH
 
 # RUN: not llvm-ifs --input-format=IFS --output-ifs=- --exclude='[' %s 2>&1 | \
 # RUN: FileCheck %s --check-prefix=BAD-GLOB
 
 # BAD-GLOB: error: invalid glob pattern: [
 
 --- !ifs-v1
 SoName: somelib.so
 IfsVersion: 3.0
+Target: x86_64-unknown-linux-gnu
 Symbols:
   - { Name: dont_exclude, Type: Func, Undefined: true }
   - { Name: exclude_1, Type: Func }
   - { Name: exclude_2, Type: Func, Undefined: true }
   - { Name: no_match_not_undef, Type: Func }
 ...
 
 # CHECK:      Symbols:
 # CHECK-NEXT:   - { Name: dont_exclude, Type: Func, Undefined: true }
 # CHECK-NEXT:   - { Name: no_match_not_undef, Type: Func }
 # CHECK-NEXT: ...
 
 # BOTH:       Symbols:
 # BOTH-NEXT:    - { Name: no_match_not_undef, Type: Func }
 # BOTH-NEXT:  ...

llvm/tools/llvm-ifs/llvm-ifs.cpp

int main(int argc, char *argv[]) {
   Error OverrideError = overrideIFSTarget(
       Stub, OverrideArch, OverrideEndianness, OverrideBitWidth, OverrideTriple);
   if (OverrideError)
     fatalError(std::move(OverrideError));
 
   if (StripNeededLibs)
     Stub.NeededLibs.clear();
 
+  if (Error E = filterIFSSyms(Stub, StripUndefined, ExcludeSyms))
+    fatalError(std::move(E));
+
   if (OutputELFFilePath.getNumOccurrences() == 0 &&
       OutputIFSFilePath.getNumOccurrences() == 0 &&
       OutputTBDFilePath.getNumOccurrences() == 0) {
     if (OutputFormat.getNumOccurrences() == 0) {
       WithColor::error() << "at least one output should be specified.";
       return -1;
     }
   } else if (OutputFormat.getNumOccurrences() == 1) {
case FileFormat::IFS: {
               "Triple hint does not match the actual bit width", HintEC));
 
         stripIFSTarget(Stub, true, false, false, false);
         Stub.Target.Triple = OptTargetTripleHint.getValue();
       } else {
         stripIFSTarget(Stub, StripIFSTarget, StripIFSArch,
                        StripIFSEndiannessWidth, StripIFSBitWidth);
       }
-      if (Error E = filterIFSSyms(Stub, StripUndefined, ExcludeSyms))
-        fatalError(std::move(E));
       Error IFSWriteError = writeIFS(OutputFilePath.getValue(), Stub);
       if (IFSWriteError)
         fatalError(std::move(IFSWriteError));
       break;
     }
     case FileFormat::ELF: {
       Error TargetError = validateIFSTarget(Stub, true);
       if (TargetError)
if (OutputIFSFilePath.getNumOccurrences() == 1) {
               "Triple hint does not match the actual bit width", HintEC));
 
         stripIFSTarget(Stub, true, false, false, false);
         Stub.Target.Triple = OptTargetTripleHint.getValue();
       } else {
         stripIFSTarget(Stub, StripIFSTarget, StripIFSArch,
                        StripIFSEndiannessWidth, StripIFSBitWidth);
       }
-      if (Error E = filterIFSSyms(Stub, StripUndefined, ExcludeSyms))
-        fatalError(std::move(E));
       Error IFSWriteError = writeIFS(OutputIFSFilePath.getValue(), Stub);
       if (IFSWriteError)
         fatalError(std::move(IFSWriteError));
     }
     if (OutputTBDFilePath.getNumOccurrences() == 1) {
       std::error_code SysErr;
       raw_fd_ostream Out(OutputTBDFilePath, SysErr);
       if (SysErr) {