Resolves: #2060191 Exit failed build asap

firefox.spec

@@ -897,9 +897,9 @@ ls %{_buildrootdir}
 export MACH_USE_SYSTEM_PYTHON=1
 %if 0%{?use_llvmts}
   #scl enable llvm-toolset-%{llvm_version} './mach build -v'
-  ./mach build -v
+  ./mach build -v || exit 1
 %else
-  ./mach build -v
+  ./mach build -v || exit 1
 %endif
 # Look for the reason we get: /usr/lib/rpm/debugedit: canonicalization unexpectedly shrank by one character
 readelf -wl objdir/dist/bin/libxul.so | grep "/"