[llvm-config] Don't use PATH_MAX

It doesn't exist on Windows. The number we use here doesn't really matter,
the storage will expand automatically but 256 seems like a reasonable default.
Should fix windows buildbots that complained about rL304458.

llvm-svn: 304468
diff --git a/llvm/tools/llvm-config/llvm-config.cpp b/llvm/tools/llvm-config/llvm-config.cpp
index 888da71..08b096a 100644
--- a/llvm/tools/llvm-config/llvm-config.cpp
+++ b/llvm/tools/llvm-config/llvm-config.cpp
@@ -333,7 +333,7 @@
   } else {
     ActivePrefix = CurrentExecPrefix;
     ActiveIncludeDir = ActivePrefix + "/include";
-    SmallString<PATH_MAX> path(StringRef(LLVM_TOOLS_INSTALL_DIR));
+    SmallString<256> path(StringRef(LLVM_TOOLS_INSTALL_DIR));
     sys::fs::make_absolute(ActivePrefix, path);
     ActiveBinDir = path.str();
     ActiveLibDir = ActivePrefix + "/lib" + LLVM_LIBDIR_SUFFIX;