CI: cross-compile: Allow to set CPU capabilities

The cross-compile CI tests use cross-compilers for building
and QEMU for testing. This implies that testing of ISA extension
for HW accelerated cryptographic calculations is undefined
(it depends on arch-specific QEMU defaults and arch-specific
detection mechanisms in OpenSSL).

Let's add a mechanism to set two environment variables, that allow
to control the ISA extensions:
* QEMU_CPU: used by QEMU to specify CPU capabilities of the emulation
* OPENSSL_*: used by OpenSSL (on some architectures) to enable ISA
  extensions.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20107)

.github/workflows/cross-compiles.yml

@@ -30,6 +30,15 @@ jobs:
         #          to never run the tests, otherwise its value is passed to
         #          the "make test" command to allow selective disabling of
         #          tests.
+        #   qemucpu: optional; string that describes CPU properties.
+        #            The string will be used to set the QEMU_CPU variable.
+        #   opensslcapsname: optional; string that describes the postfix of the
+        #                    OpenSSL environment variable that defines CPU
+        #                    capabilities. E.g. "foo" will result in an
+        #                    environment variable with the name OPENSSL_foo.
+        #   opensslcaps: optional; if opensslcapsname (see above) is set, then
+        #                this string will be used as content for the OpenSSL
+        #                capabilities variable.
         platform: [
           {
             arch: aarch64-linux-gnu,
@@ -164,6 +173,15 @@ jobs:
       if: github.event_name == 'push' && matrix.platform.tests != 'none'
       run: sudo apt-get -yq --force-yes install qemu-user
 
+    - name: Set QEMU environment
+      if: github.event_name == 'push' && matrix.platform.qemucpu != ''
+      run: echo "QEMU_CPU=${{ matrix.platform.qemucpu }}" >> $GITHUB_ENV
+
+    - name: Set OpenSSL caps environment
+      if: github.event_name == 'push' && matrix.platform.opensslcapsname != ''
+      run: echo "OPENSSL_${{ matrix.platform.opensslcapsname }}=\
+                 ${{ matrix.platform.opensslcaps }}" >> $GITHUB_ENV
+
     - name: make all tests
       if: github.event_name == 'push' && matrix.platform.tests == ''
       run: |