flambda-backend: Ports runtime of #154 (Add -mbranches-within-32B to major GC compilation) (#2055)

Author: riaqn

Makefile

@@ -1012,6 +1012,11 @@ $(RUNTIME_DIR)/%.npic.$(O): OC_CFLAGS += $(OC_NATIVE_CFLAGS) $(SHAREDLIB_CFLAGS)
 $(RUNTIME_DIR)/%.npic.$(O): OC_CPPFLAGS += $(OC_NATIVE_CPPFLAGS)
 $(DEPDIR)/$(RUNTIME_DIR)/%.npic.$(D): OC_CPPFLAGS += $(OC_NATIVE_CPPFLAGS)
 
+# The major GC performs better with this flag on Intel processors
+# This is a workaround for an Intel CPU bug:
+# https://www.intel.co.uk/content/www/uk/en/support/articles/000055650/processors.html
+$(RUNTIME_DIR)/major_gc.$(O): OC_CFLAGS += $(INTEL_JCC_BUG_CFLAGS)
+
 ## Compilation of runtime C files
 
 # The COMPILE_C_FILE macro below receives as argument the pattern