Documentation: Add a mention of the recent requirement for a newer

host compiler. On macOS this might have to be specified explicitly.

Documentation/BuildInstructions.md

@@ -42,16 +42,8 @@ Ensure your CMake version is >= 3.16 with `cmake --version`. If your system does
 #### macOS prerequisites
 Make sure you have all the dependencies installed:
 ```bash
-brew install coreutils
 brew tap discoteq/discoteq
-brew install flock
-brew install qemu
-brew install e2fsprogs
-brew install m4
-brew install autoconf
-brew install libtool
-brew install automake
-brew install bash
+brew install coreutils flock qemu e2fsprogs m4 autoconf libtool automake bash gcc@10
 brew cask install osxfuse
 Toolchain/BuildFuseExt2.sh
 ```
@@ -65,6 +57,7 @@ Notes:
 - osxfuse, e2fsprogs, m4, autoconf, automake, libtool and `BuildFuseExt2.sh` are needed if you want to build the root filesystem disk image natively on macOS. This allows mounting an EXT2 fs and also installs commands like `mke2fs` that are not available on stock macOS. 
 - bash is needed because the default version installed on macOS doesn't support globstar
 - If you install some commercial EXT2 macOS fs handler instead of osxfuse and fuse-ext2, you will need to `brew install e2fsprogs` to obtain `mke2fs` anyway.
+- As of 2020-08-06, you might need to tell the build system about your newer host compiler. Once you've built the toolchain, navigate to `Build/`, `rm -rf *`, then run `cmake .. -DCMAKE_C_COMPILER=gcc-10 -DCMAKE_CXX_COMPILER=g++-10`, then continue with `make install` as usual.
 
 #### OpenBSD prerequisites
 ```