Recipes: make cwd default to slave_build

scripts/slave/recipes/boringssl.expected/win64.json

Index: scripts/slave/recipes/boringssl.expected/win64.json
diff --git a/scripts/slave/recipes/boringssl.expected/win64.json b/scripts/slave/recipes/boringssl.expected/win64.json
index 6c8bece7a192c9cba7fac466d47722e5068d8b02..b47680b274519e4e3e7810ad3fdf7379e0b7c088 100644
--- a/scripts/slave/recipes/boringssl.expected/win64.json
+++ b/scripts/slave/recipes/boringssl.expected/win64.json
@@ -22,6 +22,7 @@
       "boringssl@HEAD",
       "--force"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -43,6 +44,7 @@
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gclient runhooks"
   },
   {
@@ -53,6 +55,7 @@
       "[SLAVE_BUILD]\\boringssl\\build",
       "511"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "makedirs mkdir",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
@@ -96,6 +99,7 @@
       "-C",
       "[SLAVE_BUILD]\\boringssl\\build"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "ninja"
   },
   {