Revert "[clang-cl] Always interpret the LIB env var as separated with semicolons"

This reverts commit 4d85444b317a00a3e15da63cdb693d272c99a0cc.

This commit broke building lldb's NativeProcessProtocolTest.cpp,
with errors like these:

In file included from include/llvm/Support/Process.h:32:0,
                 from tools/lldb/unittests/Host/NativeProcessProtocolTest.cpp:12:
include/llvm/Support/Program.h:39:11: error: reference to ‘pid_t’ is ambiguous
   typedef pid_t procid_t;

/usr/include/sched.h:38:17: note: candidates are: typedef __pid_t pid_t
 typedef __pid_t pid_t;

tools/lldb/include/lldb/lldb-types.h:85:18: note: typedef uint64_t lldb::pid_t
 typedef uint64_t pid_t;

1 files changed, 5 insertions, 6 deletions

diff --git a/llvm/lib/Support/Process.cpp b/llvm/lib/Support/Process.cpp
index 9f0b689..9e6e233 100644
--- a/llvm/lib/Support/Process.cpp
+++ b/llvm/lib/Support/Process.cpp
@@ -28,22 +28,21 @@ using namespace sys;
 //===          independent code.
 //===----------------------------------------------------------------------===//
 
-Optional<std::string>
-Process::FindInEnvPath(StringRef EnvName, StringRef FileName, char Separator) {
-  return FindInEnvPath(EnvName, FileName, {}, Separator);
+Optional<std::string> Process::FindInEnvPath(StringRef EnvName,
+                                             StringRef FileName) {
+  return FindInEnvPath(EnvName, FileName, {});
 }
 
 Optional<std::string> Process::FindInEnvPath(StringRef EnvName,
                                              StringRef FileName,
-                                             ArrayRef<std::string> IgnoreList,
-                                             char Separator) {
+                                             ArrayRef<std::string> IgnoreList) {
   assert(!path::is_absolute(FileName));
   Optional<std::string> FoundPath;
   Optional<std::string> OptPath = Process::GetEnv(EnvName);
   if (!OptPath.hasValue())
     return FoundPath;
 
-  const char EnvPathSeparatorStr[] = {Separator, '\0'};
+  const char EnvPathSeparatorStr[] = {EnvPathSeparator, '\0'};
   SmallVector<StringRef, 8> Dirs;
   SplitString(OptPath.getValue(), Dirs, EnvPathSeparatorStr);