moved conditional logic around download/install into make (vs. qmake)

QGCExternalLibs.pri

@@ -230,32 +230,27 @@ contains (DEFINES, DISABLE_AIRMAP) {
             DEFINES += QGC_AIRMAP_ENABLED
         }
     } else:LinuxBuild {
-        exists("$${AIRMAP_PLATFORM_SDK_PATH}/linux/$$AIRMAP_QT_PATH") {
-            #-- We have a cached copy..don't download and install again
-            LIBS += -L$${AIRMAP_PLATFORM_SDK_PATH}/linux/$$AIRMAP_QT_PATH -lairmap-qt
-            DEFINES += QGC_AIRMAP_ENABLED
-        } else {
-            #-- Download and install platform-sdk libs and headers
-            AIRMAP_PLATFORM_SDK_URL = "https://github.com/airmap/platform-sdk/releases/download/v1.1/airmap-platform-sdk-1.1.0-Linux.deb"
-            AIRMAP_PLATFORM_SDK_FILENAME = "airmap-platform-sdk.deb"
-            AIRMAP_PLATFORM_SDK_INSTALL_PREFIX = "airmap-platform-sdk"
+        #-- Download and install platform-sdk libs and headers iff they're not already in the build directory
+        AIRMAP_PLATFORM_SDK_URL = "https://github.com/airmap/platform-sdk/releases/download/v1.1/airmap-platform-sdk-1.1.0-Linux.deb"
+        AIRMAP_PLATFORM_SDK_FILENAME = "airmap-platform-sdk.deb"
+        AIRMAP_PLATFORM_SDK_INSTALL_PREFIX = "airmap-platform-sdk"
 
-            airmap_platform_sdk_install.target = install_airmap_platform_sdk
-            airmap_platform_sdk_install.commands = \
-                (mkdir -p "$${AIRMAP_PLATFORM_SDK_PATH}/linux/$${AIRMAP_QT_PATH}") && \
-                (mkdir -p "$${AIRMAP_PLATFORM_SDK_PATH}/include/airmap") && \
-                (wget -q -O "$${OUT_PWD}/$${AIRMAP_PLATFORM_SDK_FILENAME}" "$${AIRMAP_PLATFORM_SDK_URL}" && dpkg -x "$${AIRMAP_PLATFORM_SDK_FILENAME} $${AIRMAP_PLATFORM_SDK_PATH}/") && \
-                (mv "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}/lib/*" "$${AIRMAP_PLATFORM_SDK_PATH}/linux/$${AIRMAP_QT_PATH}/") && \
-                (mv "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}/include/airmap/*" "$${AIRMAP_PLATFORM_SDK_PATH}/include/airmap/") && \
-                (rm -rf "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}") && \
-                (rm "$${AIRMAP_PLATFORM_SDK_FILENAME}")
-            airmap_platform_sdk_install.depends = ${AIRMAP_PLATFORM_SDK_PATH}
-            QMAKE_EXTRA_TARGETS += airmap_platform_sdk_install
-            PRE_TARGETDEPS += $$airmap_platform_sdk_install.target
+        airmap_platform_sdk_install.target = install_airmap_platform_sdk
+        airmap_platform_sdk_install.commands = \
+            test -e "$${AIRMAP_PLATFORM_SDK_PATH}/include/airmap" || \
+            (mkdir -p "$${AIRMAP_PLATFORM_SDK_PATH}/linux/$${AIRMAP_QT_PATH}" && \
+            mkdir -p "$${AIRMAP_PLATFORM_SDK_PATH}/include/airmap" && \
+            wget -q -O "$${OUT_PWD}/$${AIRMAP_PLATFORM_SDK_FILENAME}" "$${AIRMAP_PLATFORM_SDK_URL}" && dpkg -x "$${AIRMAP_PLATFORM_SDK_FILENAME} $${AIRMAP_PLATFORM_SDK_PATH}/" && \
+            mv -u "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}/lib/*" "$${AIRMAP_PLATFORM_SDK_PATH}/linux/$${AIRMAP_QT_PATH}/" && \
+            mv -u "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}/include/airmap/*" "$${AIRMAP_PLATFORM_SDK_PATH}/include/airmap/" && \
+            rm -rf "$${AIRMAP_PLATFORM_SDK_PATH}/$${AIRMAP_PLATFORM_SDK_INSTALL_PREFIX}" && \
+            rm "$${AIRMAP_PLATFORM_SDK_FILENAME}")
+        airmap_platform_sdk_install.depends =
+        QMAKE_EXTRA_TARGETS += airmap_platform_sdk_install
+        PRE_TARGETDEPS += $$airmap_platform_sdk_install.target
 
-            LIBS += -L$${AIRMAP_PLATFORM_SDK_PATH}/linux/$$AIRMAP_QT_PATH -lairmap-qt
-            DEFINES += QGC_AIRMAP_ENABLED
-        }
+        LIBS += -L$${AIRMAP_PLATFORM_SDK_PATH}/linux/$$AIRMAP_QT_PATH -lairmap-qt
+        DEFINES += QGC_AIRMAP_ENABLED
     } else {
         message("Skipping support for Airmap (unsupported platform)")
     }