Make it possible to create a statically-linked mold executable

Makefile

@@ -10,8 +10,8 @@ CPPFLAGS=-g -IoneTBB/include -IxxHash -pthread -std=c++20 \
          -DGIT_HASH=\"$(shell git rev-parse HEAD)\"
 LDFLAGS=-L$(TBB_LIBDIR) -Wl,-rpath=$(TBB_LIBDIR) \
         -L$(MALLOC_LIBDIR) -Wl,-rpath=$(MALLOC_LIBDIR) \
-        -L$(CURRENT_DIR)/xxHash
-LIBS=-lcrypto -pthread -ltbb -lmimalloc -lz xxHash/libxxhash.a
+        -L$(CURRENT_DIR)/xxHash -Wl,-rpath=$(CURRENT_DIR)/xxHash
+LIBS=-lcrypto -pthread -ltbb -lmimalloc -lz -lxxhash -ldl
 OBJS=main.o object_file.o input_sections.o output_chunks.o mapfile.o perf.o \
      linker_script.o archive_file.o output_file.o subprocess.o gc_sections.o \
      icf.o symbols.o cmdline.o filepath.o glob.o passes.o arch_x86_64.o \
@@ -24,6 +24,11 @@ else
   CPPFLAGS += -O2
 endif
 
+STATIC ?= 0
+ifeq ($(STATIC), 1)
+  LDFLAGS += -static
+endif
+
 all: mold mold-wrapper.so
 
 mold: $(OBJS)
@@ -36,8 +41,9 @@ $(OBJS): mold.h elf.h Makefile
 
 submodules:
 	$(MAKE) -C oneTBB
+	$(MAKE) -C oneTBB extra_inc=big_iron.inc
 	mkdir -p mimalloc/out/release
-	(cd mimalloc/out/release; cmake ../..)
+	(cd mimalloc/out/release; CFLAGS=-DMI_USE_ENVIRON=0 cmake ../..)
 	$(MAKE) -C mimalloc/out/release
 	$(MAKE) -C xxHash