[infra] Change CMake build to use a temporary directory

This prevents Docker from creating a root-owned out directory
which persists on bots and causes failures for other tasks.

Bug: skia:9749
Change-Id: I79382d3d7a4b6d8ac61a429750ff99bde20d306d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264018
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
(cherry picked from commit edae1b3e044e5755a7b05a9776525fc6a00f0f7b)
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264297
Reviewed-by: Eric Boren <borenet@google.com>

gn/gn_to_cmake.py

diff --git a/gn/gn_to_cmake.py b/gn/gn_to_cmake.py
index 7dbf82c..9375be7 100644
--- a/gn/gn_to_cmake.py
+++ b/gn/gn_to_cmake.py
@@ -162,12 +162,11 @@
     self.targets = project_json['targets']
     build_settings = project_json['build_settings']
     self.root_path = build_settings['root_path']
-    self.build_path = posixpath.join(self.root_path,
-                                     build_settings['build_dir'][2:])
+    self.build_path = self.GetAbsolutePath(build_settings['build_dir'])
 
   def GetAbsolutePath(self, path):
-    if path.startswith("//"):
-      return self.root_path + "/" + path[2:]
+    if path.startswith('//'):
+      return posixpath.join(self.root_path, path[2:])
     else:
       return path
 

infra/cmake/build_skia.sh

diff --git a/infra/cmake/build_skia.sh b/infra/cmake/build_skia.sh
index dbd50dc..cb88147 100755
--- a/infra/cmake/build_skia.sh
+++ b/infra/cmake/build_skia.sh
@@ -16,21 +16,21 @@
 
 #BASE_DIR is the dir this script is in ($SKIA_ROOT/infra/cmake)
 BASE_DIR=`cd $(dirname ${BASH_SOURCE[0]}) && pwd`
-SKIA_DIR=`cd $BASE_DIR/../.. && pwd`
+SKIA_DIR=`cd ${BASE_DIR}/../.. && pwd`
 
-# Delete everything to do a clean build
-rm -rf $SKIA_DIR/out/CMAKE
-mkdir --mode=0777 -p $SKIA_DIR/out/CMAKE
+OUT="$(mktemp -d)/CMAKE"
 
-cd $SKIA_DIR
+cd ${SKIA_DIR}
 ./bin/fetch-gn
-gn gen out/CMAKE --args='is_debug=false' --ide=json --json-ide-script=../../gn/gn_to_cmake.py
+gn gen ${OUT} --args='is_debug=false' --ide=json --json-ide-script=$SKIA_DIR/gn/gn_to_cmake.py
 
-cd $SKIA_DIR/out/CMAKE
+cd ${OUT}
+export CC=/usr/local/bin/clang
+export CXX=/usr/local/bin/clang++
 cmake -G"CodeBlocks - Unix Makefiles" .
 cmake --build . --parallel 8
 
 # Copy build products, ignoring the warning
 # for not copying directories.
-cp $SKIA_DIR/out/CMAKE/* /OUT || true
+cp ${OUT}/* /OUT || true
 chmod +rw /OUT/*