Auto merge of #37006 - brson:jsbackend, r=alexcrichton

Turn on JSBackend in the makefiles

This should make the nightlies work with emscripten. r? @alexcrichton

Closes #37004

Author: bors

configure

@@ -1764,7 +1764,7 @@ do
         CMAKE_ARGS="$CMAKE_ARGS -DLLVM_ENABLE_ASSERTIONS=ON"
     fi
 
-    CMAKE_ARGS="$CMAKE_ARGS -DLLVM_TARGETS_TO_BUILD='X86;ARM;AArch64;Mips;PowerPC;SystemZ'"
+    CMAKE_ARGS="$CMAKE_ARGS -DLLVM_TARGETS_TO_BUILD='X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend'"
     CMAKE_ARGS="$CMAKE_ARGS -G '$CFG_CMAKE_GENERATOR'"
     CMAKE_ARGS="$CMAKE_ARGS $CFG_LLVM_SRC_DIR"