configure, meson: deprecate 32-bit MIPS

The mipsel architecture is not available in Debian Trixie, and it will
likely be a hard failure as soon as we drop support for the old Rust
toolchain in Debian Bookworm.  Prepare by deprecating 32-bit little
endian MIPS in QEMU 9.2.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/about/build-platforms.rst

@@ -41,7 +41,7 @@ Those hosts are officially supported, with various accelerators:
      - Accelerators
    * - Arm
      - kvm (64 bit only), tcg, xen
-   * - MIPS (little endian only)
+   * - MIPS (64 bit little endian only)
      - kvm, tcg
    * - PPC
      - kvm, tcg

docs/about/deprecated.rst

@@ -164,15 +164,19 @@ property types.
 Host Architectures
 ------------------
 
-BE MIPS (since 7.2)
+Big endian MIPS since 7.2; 32-bit little endian MIPS since 9.2
-'''''''''''''''''''
+''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
 As Debian 10 ("Buster") moved into LTS the big endian 32 bit version of
 MIPS moved out of support making it hard to maintain our
 cross-compilation CI tests of the architecture. As we no longer have
 CI coverage support may bitrot away before the deprecation process
-completes. The little endian variants of MIPS (both 32 and 64 bit) are
+completes.
-still a supported host architecture.
+
+Likewise, the little endian variant of 32 bit MIPS is not supported by
+Debian 13 ("Trixie") and newer.
+
+64 bit little endian MIPS is still a supported host architecture.
 
 System emulation on 32-bit x86 hosts (since 8.0)
 ''''''''''''''''''''''''''''''''''''''''''''''''

meson.build

@@ -4720,6 +4720,14 @@ if host_arch == 'unknown'
     message('configure has succeeded and you can continue to build, but')
     message('QEMU will use a slow interpreter to emulate the target CPU.')
   endif
+elif host_arch == 'mips'
+  message()
+  warning('DEPRECATED HOST CPU')
+  message()
+  message('Support for CPU host architecture ' + cpu + ' is going to be')
+  message('dropped as soon as the QEMU project stops supporting Debian 12')
+  message('("Bookworm"). Going forward, the QEMU project will not guarantee')
+  message('that QEMU will compile or work on this host CPU.')
 endif
 
 if not supported_oses.contains(host_os)