Move dejagnu install step to libgccjit tests documentation

Author: winstonallo

Readme.md

@@ -57,7 +57,7 @@ To build it (most of these instructions come from [here](https://gcc.gnu.org/onl
 
 ```bash
 $ git clone https://github.com/rust-lang/gcc
-$ sudo apt install flex libmpfr-dev libgmp-dev libmpc3 libmpc-dev dejagnu
+$ sudo apt install flex libmpfr-dev libgmp-dev libmpc3 libmpc-dev
 $ mkdir gcc-build gcc-install
 $ cd gcc-build
 $ ../gcc/configure \
@@ -70,15 +70,22 @@ $ ../gcc/configure \
 $ make -j4 # You can replace `4` with another number depending on how many cores you have.
 ```
 
-If you want to run libgccjit tests, you will need to also enable the C++ language in the `configure`:
+If you want to run libgccjit tests, you will need to
+* Enable the C++ language in the `configure` step:
 
 ```bash
 --enable-languages=jit,c++
 ```
+* Install [dejagnu](https://www.gnu.org/software/dejagnu/#downloading) to run the tests
+
+```bash
+$ sudo apt install dejagnu
+```
 
 Then to run libgccjit tests:
 
 ```bash
+$ sudo apt install dejagnu
 $ cd gcc # from the `gcc-build` folder
 $ make check-jit
 # To run one specific test: