gradle: Only forward EIGEN3_INCLUDE_DIR definition if we actually have it set.

build.gradle

@@ -48,8 +48,8 @@ ext {
     sharedMinSdk = 26
 
     // If you are building on Windows, you will need to explicitly set eigenIncludeDir in your
-    // local.properties file since the default value provided below only makes sense on *nix
-    eigenIncludeDir = project.findProperty('eigenIncludeDir') ?: '/usr/include/eigen3'
+    // local.properties file
+    eigenIncludeDir = project.findProperty('eigenIncludeDir')
 
     // If you're having trouble with a "can't find python" CMake error, you can specify the path to
     // Python 3 explicitly in local.properties with a property named "pythonBinary"

src/xrt/targets/openxr_android/build.gradle

@@ -89,13 +89,17 @@ android {
 
         externalNativeBuild {
             cmake {
-                arguments "-DEIGEN3_INCLUDE_DIR=${project.eigenIncludeDir}", "-DANDROID_PLATFORM=26", "-DANDROID_STL=c++_shared", "-DANDROID_ARM_NEON=TRUE"
+                arguments "-DANDROID_PLATFORM=26", "-DANDROID_STL=c++_shared", "-DANDROID_ARM_NEON=TRUE"
 
             }
             if (project.pythonBinary != null) {
-                println "Path to Python 3 explicitly specified: ${project.pythonBinary}"
+                println "Path to Python 3 explicitly specified: pythonBinary=${project.pythonBinary}"
                 cmake.arguments "-DPYTHON_EXECUTABLE=${project.pythonBinary}"
             }
+            if (project.eigenIncludeDir != null) {
+                println "Path to Eigen3 includes explicitly specified: eigenIncludeDir=${project.eigenIncludeDir}"
+                cmake.arguments "-DEIGEN3_INCLUDE_DIR=${project.eigenIncludeDir}"
+            }
         }
 
         // Be sure to copy over licenses formatted as required.