Disable HTML docs on riscv64 for now

Signed-off-by: David Abdurachmanov <davidlt@rivosinc.com>

gn.spec

@@ -1,5 +1,9 @@
 # Build HTML docs from markdown using pandoc?
+%ifnarch riscv64
 %bcond_without html_docs
+%else
+%bcond_with html_docs
+%endif
 # Normally, treating warnings as errors is too strict for downstream builds.
 # It’s nice to be able to turn it on, though.
 %bcond_with werror
@@ -32,7 +36,7 @@ Name:           gn
 %global shortcommit %(echo '%{commit}' | cut -b -12)
 %global position 2084
 Version:        %{position}^%{access}git%{shortcommit}
-Release:        %autorelease
+Release:        %autorelease -e 0.riscv64
 Summary:        Meta-build system that generates build files for Ninja
 
 # The entire source is BSD-3-Clause, except: