Fedora 23: remove autotools-devel, add gcc-c++

Without g++, it fails in this rather opaque way:

configure: error: error verifying int64_t uses long long
Makefile:4063: recipe for target 'configure-gcc' failed
make[2]: *** [configure-gcc] Error 1
make[2]: Leaving directory '/tmp/riscv-gnu-toolchain/build-gcc-newlib'
Makefile:867: recipe for target 'all' failed
make[1]: *** [all] Error 2
make[1]: Leaving directory '/tmp/riscv-gnu-toolchain/build-gcc-newlib'
Makefile:245: recipe for target 'stamps/build-gcc-newlib' failed
make: *** [stamps/build-gcc-newlib] Error 2

README.md

@@ -14,7 +14,7 @@ executing the following command should suffice:
 
 On Fedora/CentOS/RHEL OS, executing the following command should suffice:
 
-    $ sudo yum install autoconf automake autotools-devel libmpc-devel mpfr-devel gmp-devel gawk  bison flex texinfo patchutils gcc 
+    $ sudo yum install autoconf automake libmpc-devel mpfr-devel gmp-devel gawk  bison flex texinfo patchutils gcc gcc-c++
 
 On OS X, you can use [Homebrew](http://brew.sh) to install the dependencies: