fix broken AMD APP SDK download links

AMD has removed the AMD APP SDK links from the website. The AMD employes in the AMD formum posted links to there Dropbox where the SDK can be downloaded)

doc/compile_Linux.md

@@ -4,7 +4,8 @@
 
 ### AMD APP SDK 3.0 (only needed to use AMD GPUs)
 
-- download and install the latest version from [http://developer.amd.com/amd-accelerated-parallel-processing-app-sdk/](http://developer.amd.com/amd-accelerated-parallel-processing-app-sdk/)
+- download and install the latest version from https://www.dropbox.com/sh/mpg882ekirnsfa7/AADWz5X-TgVdsmWt0QwMgTWLa/AMD-APP-SDKInstaller-v3.0.130.136-GA-linux64.tar.bz2?dl=0
+  (do not wonder why it is a link to a dropbox but AMD has removed the SDK downloads, see https://community.amd.com/thread/228059)
 
 ### Cuda 8.0+ (only needed to use NVIDIA GPUs)
 

doc/compile_Windows.md

@@ -32,7 +32,8 @@
 
 ### AMD APP SDK 3.0 (only needed for AMD GPUs)
 
-- Download and install the latest version from http://developer.amd.com/amd-accelerated-parallel-processing-app-sdk/
+- Download and install the latest version from https://www.dropbox.com/s/gq8vqhelq0m6gj4/AMD-APP-SDKInstaller-v3.0.130.135-GA-windows-F-x64.exe
+  (do not wonder why it is a link to a dropbox but AMD has removed the SDK downloads, see https://community.amd.com/thread/222855)
 
 ### Dependencies OpenSSL/Hwloc and Microhttpd
 - For CUDA 8*: