Fix parallel Gradle build problems in teapots (#1167)

When building the entire project with Gradle, if Gradle-level
inter-project parallelism is enabled (either via the property
`org.gradle.parallel=true`, or via Android Studio injected flags), then
the build was failing, because these sub-projects under the teapots
project all try to write their ndkHelper library outputs to the same
path, causing a race condition.

When we use a relative path for the output binary (instead of an
absolute path like it used to be), then AGP puts the CMake/Ninja outputs
to per-subproject folders under `$project/.cxx` which avoids the race
condition.

Author: emrekultursay

teapots/choreographer-30fps/src/main/cpp/CMakeLists.txt

@@ -24,7 +24,7 @@ find_package(base CONFIG REQUIRED)
 get_filename_component(commonDir ${CMAKE_CURRENT_SOURCE_DIR}/../../../../common ABSOLUTE)
 get_filename_component(ndkHelperSrc ${commonDir}/ndk_helper ABSOLUTE)
 add_subdirectory(${ndkHelperSrc}
-    ${commonDir}/ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
+    ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
 
 # now build app's shared lib
 add_app_library(${PROJECT_NAME}

teapots/classic-teapot/src/main/cpp/CMakeLists.txt

@@ -23,7 +23,7 @@ include(AppLibrary)
 get_filename_component(commonDir ${CMAKE_CURRENT_SOURCE_DIR}/../../../../common ABSOLUTE)
 get_filename_component(ndkHelperSrc ${commonDir}/ndk_helper ABSOLUTE)
 add_subdirectory(${ndkHelperSrc}
-    ${commonDir}/ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
+    ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
 
 # now build app's shared lib
 add_app_library(${PROJECT_NAME}

teapots/image-decoder/src/main/cpp/CMakeLists.txt

@@ -24,7 +24,7 @@ get_filename_component(commonDir ${CMAKE_CURRENT_SOURCE_DIR}/../../../../common
 # build the ndk-helper library
 get_filename_component(ndkHelperSrc ${commonDir}/ndk_helper ABSOLUTE)
 add_subdirectory(${ndkHelperSrc}
-    ${commonDir}/ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
+    ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
 
 # now build app's shared lib
 add_app_library(${PROJECT_NAME}

teapots/more-teapots/src/main/cpp/CMakeLists.txt

@@ -23,7 +23,7 @@ include(AppLibrary)
 get_filename_component(commonDir ${CMAKE_CURRENT_SOURCE_DIR}/../../../../common ABSOLUTE)
 get_filename_component(ndkHelperSrc ${commonDir}/ndk_helper ABSOLUTE)
 add_subdirectory(${ndkHelperSrc}
-    ${commonDir}/ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
+    ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
 
 
 # now build app's shared lib

teapots/textured-teapot/src/main/cpp/CMakeLists.txt

@@ -31,7 +31,7 @@ endif()
 # build the ndk-helper library
 get_filename_component(ndkHelperSrc ${commonDir}/ndk_helper ABSOLUTE)
 add_subdirectory(${ndkHelperSrc}
-    ${commonDir}/ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
+    ndkHelperBin/${CMAKE_BUILD_TYPE}/${ANDROID_ABI})
 
 # now build app's shared lib
 add_app_library(${PROJECT_NAME}