117610218: Flaky build error caused by metalava using same temporary directory

Take 2: Always create unique directory when TMPDIR is set.

Change-Id: Ib4d33d3adf3a02baf5d3b2dcd8f8ef82257196a4
Fixes: 117610218
Test: Manually set TMPDIR and verified result
diff --git a/.idea/kotlinc.xml b/.idea/kotlinc.xml
new file mode 100644
index 0000000..8b7f4af
--- /dev/null
+++ b/.idea/kotlinc.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Kotlin2JsCompilerArguments">
+    <option name="sourceMapEmbedSources" />
+  </component>
+</project>
\ No newline at end of file