template/prelude.c.tmpl: suppress clang-12 warning

Clang 12 warns "suspicious concatenation of string literals in an array
initialization", which is rather annoying than useful in this context.

template/prelude.c.tmpl

@@ -81,6 +81,10 @@ Prelude.new(output, ARGV, vpath).instance_eval do
 #include "ruby/ruby.h"
 #include "vm_core.h"
 
+COMPILER_WARNING_PUSH
+#if __has_warning("-Wstring-concatenation")
+COMPILER_WARNING_IGNORED(-Wstring-concatenation)
+#endif
 % preludes = @preludes.values.sort
 % preludes.each {|i, prelude, lines, sub|
 
@@ -116,6 +120,8 @@ static const struct {
 };
 % }
 
+COMPILER_WARNING_POP
+
 % if @have_sublib
 #define PRELUDE_COUNT <%=preludes.size%>