More makefile magic

This time for the llvm configuration.

Sometimes when updating the LLVM directory, we need to reconfigure things.
We don't know that until after we update it, though, but Make will decide
at the beginning whether it needs to be updated or not.  We could always
reconfigure every time we update LLVM (might be ok), or add a helper
target that recursively calls Make after the updating is done (what this
patch does).

This should fix those "C compiler can't generate executables" errors that
come from running two copies of the configure script in parallel.

src/Makefile

@@ -408,13 +408,13 @@ Makefile.local:
 
 LLVM_CONFIGURATION := $(LLVM_BUILD)/Makefile.config
 # First, specify when we need to rebuild the different targets:
-$(LLVM_BUILD)/built_quick: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+$(LLVM_BUILD)/built_quick: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	$(MAKE) llvm_quick
-$(LLVM_BUILD)/built_debug: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+$(LLVM_BUILD)/built_debug: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	$(MAKE) llvm_debug
-$(LLVM_BUILD)/built_release: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+$(LLVM_BUILD)/built_release: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	$(MAKE) llvm_release
-$(LLVM_BUILD)/built_profile: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+$(LLVM_BUILD)/built_profile: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	$(MAKE) llvm_profile
 # Now, specify that we shouldn't check the timestamps of dependencies until after
 # the llvm rebuild finishes, if one is happening, but do it with order-only
@@ -469,7 +469,11 @@ ifneq ($(ENABLE_INTEL_JIT_EVENTS),0)
 LLVM_CONFIGURE_LINE += --with-intel-jitevents
 endif
 
-$(LLVM_CONFIGURATION): $(LLVM_SRC)/configure $(LLVM_CONFIG_INCL) | $(LLVM_SRC)/_patched
+.PHONY: llvm_configure_if_needed
+llvm_configure_if_needed: $(LLVM_SRC)/_patched
+	$(MAKE) $(LLVM_CONFIGURATION)
+
+$(LLVM_CONFIGURATION): $(LLVM_SRC)/configure $(LLVM_CONFIG_INCL)
 	mkdir -p $(LLVM_BUILD)
 	cd $(LLVM_BUILD) ; \
 	$(LLVM_CONFIGURE_LINE)
@@ -536,19 +540,19 @@ llvm_test_release: llvm_release
 llvm_test_all: llvm_release
 	$(MAKE) -C $(LLVM_BUILD) ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1 check-all
 
-llvm/quick/%: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+llvm/quick/%: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	mkdir -p $(patsubst llvm/quick/%,$(LLVM_BUILD)/%,$@)
 	$(VERB) if [ ! -f $(patsubst llvm/quick/%,$(LLVM_BUILD)/%/Makefile,$@) ]; then cp $(patsubst llvm/quick/%,$(LLVM_SRC)/%/Makefile,$@) $(patsubst llvm/quick/%,$(LLVM_BUILD)/%/,$@); fi
 	$(LLVM_BUILD_ENV) $(MAKE) -C $(patsubst llvm/quick/%,$(LLVM_BUILD)/%,$@) $(LLVM_BUILD_VARS) ENABLE_OPTIMIZED=1 DEBUG_RUNTIME=0 NO_DEBUG_SYMBOLS=1
-llvm/release/%: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+llvm/release/%: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	mkdir -p $(patsubst llvm/release/%,$(LLVM_BUILD)/%,$@)
 	$(VERB) if [ ! -f $(patsubst llvm/release/%,$(LLVM_BUILD)/%/Makefile,$@) ]; then cp $(patsubst llvm/release/%,$(LLVM_SRC)/%/Makefile,$@) $(patsubst llvm/release/%,$(LLVM_BUILD)/%/,$@); fi
 	$(LLVM_BUILD_ENV) $(MAKE) -C $(patsubst llvm/release/%,$(LLVM_BUILD)/%,$@) $(LLVM_BUILD_VARS) ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1
-llvm/debug/%: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+llvm/debug/%: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	mkdir -p $(patsubst llvm/debug/%,$(LLVM_BUILD)/%,$@)
 	$(VERB) if [ ! -f $(patsubst llvm/debug/%,$(LLVM_BUILD)/%/Makefile,$@) ]; then cp $(patsubst llvm/debug/%,$(LLVM_SRC)/%/Makefile,$@) $(patsubst llvm/debug/%,$(LLVM_BUILD)/%/,$@); fi
 	$(LLVM_BUILD_ENV) $(MAKE) -C $(patsubst llvm/debug/%,$(LLVM_BUILD)/%,$@) $(LLVM_BUILD_VARS) DEBUG_RUNTIME=1 DEBUG_SYMBOLS=1 ENABLE_OPTIMIZED=0
-llvm/profile/%: $(LLVM_SRC)/_patched $(LLVM_CONFIGURATION)
+llvm/profile/%: $(LLVM_SRC)/_patched llvm_configure_if_needed
 	mkdir -p $(patsubst llvm/profile/%,$(LLVM_BUILD)/%,$@)
 	$(VERB) if [ ! -f $(patsubst llvm/profile/%,$(LLVM_BUILD)/%/Makefile,$@) ]; then cp $(patsubst llvm/profile/%,$(LLVM_SRC)/%/Makefile,$@) $(patsubst llvm/profile/%,$(LLVM_BUILD)/%/,$@); fi
 	$(LLVM_BUILD_ENV) $(MAKE) -C $(patsubst llvm/profile/%,$(LLVM_BUILD)/%,$@) $(LLVM_BUILD_VARS) CXXFLAGS="-fno-omit-frame-pointer -fno-function-sections" ENABLE_PROFILING=1 ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1 $(LLVM_MAKE_ARGS)