Remove support for single-precision Bullet, fail during configuration instead of during linking.

cmake/CheckBulletPrecision.cmake

@@ -0,0 +1,45 @@
+set(TMP_ROOT ${CMAKE_BINARY_DIR}/try-compile)
+file(MAKE_DIRECTORY ${TMP_ROOT})
+
+file(WRITE ${TMP_ROOT}/checkbullet.cpp
+"
+#include <BulletCollision/CollisionShapes/btSphereShape.h>
+int main(int argc, char** argv)
+{
+    btSphereShape shape(1.0);
+    btScalar mass(1.0);
+    btVector3 inertia;
+    shape.calculateLocalInertia(mass, inertia);
+    return 0;
+}
+")
+
+file(WRITE ${TMP_ROOT}/CMakeLists.txt
+"
+cmake_minimum_required(VERSION 3.1.0)
+project(checkbullet)
+add_executable(checkbullet checkbullet.cpp)
+find_package(Bullet REQUIRED COMPONENTS BulletCollision LinearMath)
+target_compile_definitions(checkbullet PUBLIC BT_USE_DOUBLE_PRECISION)
+include_directories(\$\{BULLET_INCLUDE_DIRS\})
+include(${CMAKE_SOURCE_DIR}/cmake/OSIdentity.cmake)
+if (UBUNTU_FOUND OR DEBIAN_FOUND)
+    target_link_libraries(checkbullet BulletCollision-float64 LinearMath-float64)
+else()
+    target_link_libraries(checkbullet \$\{BULLET_LIBRARIES\})
+endif()
+")
+
+if (DEFINED BULLET_ROOT)
+    set(ROOT "-DBULLET_ROOT=${BULLET_ROOT}")
+endif()
+
+message(STATUS "Checking if Bullet uses double precision")
+
+try_compile(RESULT_VAR
+    ${CMAKE_BINARY_DIR}/temp
+    ${TMP_ROOT}
+    checkbullet
+    CMAKE_FLAGS  "${ROOT}"
+    )
+set(HAS_DOUBLE_PRECISION_BULLET ${RESULT_VAR})