Simplify the bullet detection. This way we don't need to explicitly pass

all possible variables to the try_compile stuff

cmake/CheckBulletPrecision.cmake

@@ -14,37 +14,13 @@ int main(int argc, char** argv)
 }
 ")
 
-file(WRITE ${TMP_ROOT}/CMakeLists.txt
-"
-cmake_minimum_required(VERSION 3.1.0)
-project(checkbullet)
-
-# First, try BulletConfig-float64.cmake which comes with Debian derivatives.
-find_package(Bullet CONFIGS BulletConfig-float64.cmake QUIET COMPONENTS BulletCollision LinearMath)
-if (BULLET_FOUND)
-    # Fix the relative include:
-    set(BULLET_INCLUDE_DIRS \"\$\{BULLET_ROOT_DIR\}/\$\{BULLET_INCLUDE_DIRS\}\")
-else()
-    find_package(Bullet REQUIRED COMPONENTS BulletCollision LinearMath)
-endif()
-string(REGEX MATCHALL \"((optimized|debug);)?[^;]*(BulletCollision|LinearMath)[^;]*\" BULLET_LIBRARIES \"$\{BULLET_LIBRARIES\}\")
-
-add_executable(checkbullet checkbullet.cpp)
-target_compile_definitions(checkbullet PUBLIC BT_USE_DOUBLE_PRECISION)
-target_include_directories(checkbullet PUBLIC \$\{BULLET_INCLUDE_DIRS\})
-target_link_libraries(checkbullet \$\{BULLET_LIBRARIES\})
-")
-
-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}/temp
-    ${TMP_ROOT}
+    ${TMP_ROOT}/checkbullet.cpp
-    checkbullet
+    COMPILE_DEFINITIONS "-DBT_USE_DOUBLE_PRECISION"
-    CMAKE_FLAGS  "${ROOT}"
+    LINK_LIBRARIES ${BULLET_LIBRARIES}
+    CMAKE_FLAGS  "-DINCLUDE_DIRECTORIES=${BULLET_INCLUDE_DIRS}"
     )
 set(HAS_DOUBLE_PRECISION_BULLET ${RESULT_VAR})