tests: add extra repositories to allow installation of ninja/libstdc++

tests/build-gating.fmf

@@ -24,6 +24,27 @@ adjust:
       WITH_SCL: "scl enable llvm-toolset-13.0 rust-toolset-1.58"
     when: "collection == llvm-toolset-13.0"
 
+  # Unfortunatelly, TMT does not support more declarative approach, we need to run commands on our own.
+  - because: "On RHEL, CRB must be enabled to provide rarer packages"
+    prepare+:
+      - name: Enable CRB
+        how: shell
+        script: dnf config-manager --set-enabled rhel-CRB
+    when: >-
+      distro == centos
+      or distro == rhel-9
+      or distro == rhel-8
+
+  # Unfortunatelly, TMT does not support more declarative approach, we need to run commands on our own.
+  - because: "On RHEL-7, EPEL must be enabled to provided rarer packages"
+    prepare+:
+      - name: Enable EPEL
+        how: shell
+        script: |
+          rpm -q epel-release || yum install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
+          yum-config-manager --enable epel
+    when: distro == rhel-7
+
 discover:
     how: fmf
 execute:

tests/integration-test-suite/main.fmf

@@ -3,9 +3,10 @@ description: |
   Run the upstream LLVM integration test suite
 test: "$WITH_SCL ./test.sh"
 require:
-  - ninja-build
   - git
   - make
+  # These require special repositories to be enabled on RHEL
+  - ninja-build
   - libstdc++-static
 adjust:
   # Common requirements when LLVM is not SCL-ized
@@ -46,5 +47,7 @@ adjust:
 
   - environment+:
       CMAKE_CXXLIB: "-DENABLE_LIBCXX=OFF"
-    when: "distro == rhel"
+    when: >-
-    because: libcxx is not shipped with RHEL
+      distro == centos
+      or distro == rhel
+    because: libcxx is not shipped with neither Centos nor RHEL