Fix finding llvm src dir for current emsdk layout

tools/shared.py

@@ -312,10 +312,16 @@ def check_llvm_version():
 # look for emscripten-version.txt files under or alongside the llvm source dir
 def get_fastcomp_src_dir():
   d = LLVM_ROOT
+  emroot = path_from_root() # already abspath
+  # look for version file in llvm repo, making sure not to mistake the emscripten repo for it
   while d != os.path.dirname(d):
-    # look for version file in llvm repo, making sure not to mistake the emscripten repo for it
-    if os.path.exists(os.path.join(d, 'emscripten-version.txt')) and not os.path.abspath(d) == os.path.abspath(path_from_root()):
+    d = os.path.abspath(d)
+    # when the build directory lives below the source directory
+    if os.path.exists(os.path.join(d, 'emscripten-version.txt')) and not d == emroot:
       return d
+    # when the build directory lives alongside the source directory
+    elif os.path.exists(os.path.join(d, 'src', 'emscripten-version.txt')) and not os.path.join(d, 'src') == emroot:
+      return os.path.join(d, 'src')
     else:
       d = os.path.dirname(d)
   return None