buildMozillaMach: stop polluting the hg tree

Moves the MOZ_OBJDIR into a path that is ignored through .hgignore, and
the MOZBUILD_STATE_PATH outside of the source root.

Closes: #306937

pkgs/applications/networking/browsers/firefox/common.nix

@@ -308,8 +308,8 @@ buildStdenv.mkDerivation {
     export MOZ_BUILD_DATE=$(head -n1 sourcestamp.txt)
 
     # Set predictable directories for build and state
-    export MOZ_OBJDIR=$(pwd)/mozobj
-    export MOZBUILD_STATE_PATH=$(pwd)/mozbuild
+    export MOZ_OBJDIR=$(pwd)/objdir
+    export MOZBUILD_STATE_PATH=$TMPDIR/mozbuild
 
     # Don't try to send libnotify notifications during build
     export MOZ_NOSPAM=1
@@ -353,7 +353,7 @@ buildStdenv.mkDerivation {
       # since the profiling build has not been installed to $out
       ''
         OLD_LDFLAGS="$LDFLAGS"
-        LDFLAGS="-Wl,-rpath,$(pwd)/mozobj/dist/${binaryName}"
+        LDFLAGS="-Wl,-rpath,$(pwd)/objdir/dist/${binaryName}"
       ''}
     fi
   '' + lib.optionalString googleAPISupport ''
@@ -510,7 +510,7 @@ buildStdenv.mkDerivation {
   '';
 
   preBuild = ''
-    cd mozobj
+    cd objdir
   '';
 
   postBuild = ''
@@ -535,9 +535,9 @@ buildStdenv.mkDerivation {
   preInstall = lib.optionalString crashreporterSupport ''
     ./mach buildsymbols
     mkdir -p $symbols/
-    cp mozobj/dist/*.crashreporter-symbols.zip $symbols/
+    cp objdir/dist/*.crashreporter-symbols.zip $symbols/
   '' + ''
-    cd mozobj
+    cd objdir
   '';
 
   postInstall = ''