[hotfix PATCH-for-8.1] meson: Fix cross-building for RISCV host

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

While when building on native Linux the host architecture
is reported as "riscv32" or "riscv64", when cross-compiling
it is detected as "riscv". Meson handles the cross-detection
but displays a warning:

  WARNING: Unknown CPU family riscv, please report this at https://github.com/mesonbuild/meson/issues/new

Commit 278c1bcef5 was tested on native host but not under
cross environment, and now we get there [*]:

  ../meson.build:684:6: ERROR: Problem encountered: Unsupported CPU riscv, try --enable-tcg-interpreter

Instead of:

  Found pkg-config: /usr/bin/riscv64-linux-gnu-pkg-config (1.8.1)

As a kludge, re-introduce "riscv" in the supported_cpus[] array.

Fixes: 278c1bcef5 ("target/riscv: Only unify 'riscv32/64' -> 'riscv' for host cpu in meson")
Reported-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 5fcdb37a71..58e35febb9 100644
--- a/meson.build
+++ b/meson.build
@@ -55,7 +55,7 @@ qapi_trace_events = []
 
 bsd_oses = ['gnu/kfreebsd', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'darwin']
 supported_oses = ['windows', 'freebsd', 'netbsd', 'openbsd', 'darwin', 'sunos', 'linux']
-supported_cpus = ['ppc', 'ppc64', 's390x', 'riscv32', 'riscv64', 'x86', 'x86_64',
+supported_cpus = ['ppc', 'ppc64', 's390x', 'riscv', 'riscv32', 'riscv64', 'x86', 'x86_64',
   'arm', 'aarch64', 'loongarch64', 'mips', 'mips64', 'sparc64']
 
 cpu = host_machine.cpu_family()
-- 
2.38.1