Merge pull request #3006 from bilke/bump-gcc

Bump gcc version to 9

scripts/cmake/CompilerSetup.cmake

@@ -74,9 +74,11 @@ if(COMPILER_IS_GCC OR COMPILER_IS_CLANG OR COMPILER_IS_INTEL)
     endif()
 
     if(COMPILER_IS_GCC)
-        if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${ogs.minimum_version.gcc})
-            message(FATAL_ERROR "Aborting: GCC ${ogs.minimum_version.gcc} is \
-                required! Found version ${CMAKE_CXX_COMPILER_VERSION}.")
+        if(NOT "${HOSTNAME}" MATCHES "frontend.*") # TODO: remove later
+            if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${ogs.minimum_version.gcc})
+                message(FATAL_ERROR "Aborting: GCC ${ogs.minimum_version.gcc} is \
+                    required! Found version ${CMAKE_CXX_COMPILER_VERSION}.")
+            endif()
         endif()
         add_compile_options(-fext-numeric-literals)
         include(GCCSanitizer)

web/content/docs/devguide/getting-started/prerequisites.pandoc

@@ -50,6 +50,32 @@ You need to have at least **gcc {{< dataFile "versions.minimum_version.gcc" >}}*
 $ gcc --version
 gcc (GCC) {{< dataFile "versions.minimum_version.gcc" >}}.0
 ```
+
+::: {.note}
+### Install a newer compiler on Ubuntu
+
+We recommend using Ubuntu {{< dataFile "versions.tested_version.ubuntu" >}} as its standard `gcc` package is already at version 9. If you are on an older Ubuntu version you can install a newer compiler from the `ubuntu-toolchain-r/test`-repository:
+
+```bash
+sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+sudo apt-get update
+sudo apt-get install gcc-9 g++-9
+```
+
+To make the newly installed compiler the default one:
+
+```bash
+sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 60 \
+  --slave /usr/bin/g++ g++ /usr/bin/g++-9
+```
+
+If you do not do this you have to specify the compiler during the first CMake run:
+
+```bash
+CC=gcc-9 CXX=c++-9 cmake ../ogs [more CMake options]
+```
+:::
+
 :::
 
 ::: {.mac}

web/data/versions.json

 {
   "minimum_version": {
-    "gcc": "8.0",
+    "gcc": "9.0",
     "clang": "9.0",
     "msvc": {
       "year": "2019",
@@ -22,6 +22,7 @@
     "qt": {
       "linux": "5.14.1",
       "win": "5.13.2"
-    }
+    },
+    "ubuntu": "20.04"
   }
 }