avoid parallel make on i686 in the hope of getting a build without OOM

vulkan-validation-layers.spec

@@ -45,6 +45,9 @@ developing applications that use %{name}.
 # Decrease debuginfo verbosity to reduce memory consumption even more
 %global optflags %(echo %{optflags} | sed 's/-g /-g1 /')
 
+%ifarch %{ix86}
+%global parallel -j1
+%endif
 
 %cmake3 -DCMAKE_BUILD_TYPE=Release \
         -DGLSLANG_INSTALL_DIR=%{_prefix} \
@@ -52,7 +55,7 @@ developing applications that use %{name}.
         -DUSE_ROBIN_HOOD_HASHING:BOOL=OFF \
         -DSPIRV_HEADERS_INSTALL_DIR=%{_includedir}/spirv \
         -DCMAKE_INSTALL_INCLUDEDIR=%{_includedir}/vulkan/
-%cmake_build
+%cmake_build %{?parallel}
 
 
 %install