Merge "Allow USE_GOMA=true without explicit USE_NINJA=true"

diff --cc core/goma.mk
index 7fc6c46,5b5830c..ff95d5a
--- 1/core/goma.mk
--- 2/core/goma.mk
+++ b/core/goma.mk
@@@ -16,25 -16,16 +16,26 @@@
  
  # Notice: this works only with Google's Goma build infrastructure.
  ifneq ($(USE_GOMA),)
-   # Check if USE_NINJA is defined because GNU make won't work well
-   # with goma. Note this file is evaluated twice, once with
-   # USE_NINJA=true by GNU make and once with USE_NINJA=false by kati
-   # which is invoked by GNU make. So, we cannot test the value of
-   # USE_NINJA.
-   ifndef USE_NINJA
-     $(error USE_GOMA=true works only with USE_NINJA=true)
+   # Check if USE_NINJA is not false because GNU make won't work well
+   # with goma. Note this file is evaluated twice, once by GNU make and
+   # once by kati with USE_NINJA=false. We do this check in the former
+   # pass.
+   ifndef KATI
+     ifeq ($(USE_NINJA),false)
+       $(error USE_GOMA=true is not compatible with USE_NINJA=false)
+     endif
    endif
  
 +  # Goma requires a lot of processes and file descriptors.
 +  ifeq ($(shell echo $$(($$(ulimit -u) < 2500 || $$(ulimit -n) < 16000))),1)
 +    $(warning Max user processes and/or open files are insufficient)
 +    ifeq ($(shell uname),Darwin)
 +      $(error See go/ma/how-to-use-goma/how-to-use-goma-for-android to relax the limit)
 +    else
 +      $(error Adjust the limit by ulimit -u and ulimit -n)
 +    endif
 +  endif
 +
    ifdef GOMA_DIR
      goma_dir := $(GOMA_DIR)
    else