Revamp and simplify the libpreopen code. (WebAssembly#110)

wasi-libc's copy of libpreopen has evolved so many local changes that
it's no longer worth keeping the upstream code structure and marking
changes with __wasilibc_unmodified_upstream.

This PR merges the source files into a single file, removes all
__wasilibc_unmodified_upstream code, eliminates the ability to
allocate multiple preopen lists, eliminates the need for
__wasilibc_init_preopen, eliminates the non-standard eaccess, and
makes several other cleanups. It also enables NDEBUG so that internal
assertions are disabled in release builds.

Makefile

@@ -3,7 +3,7 @@
 WASM_CC ?= clang
 WASM_NM ?= $(patsubst %clang,%llvm-nm,$(WASM_CC))
 WASM_AR ?= $(patsubst %clang,%llvm-ar,$(WASM_CC))
-WASM_CFLAGS ?= -O2
+WASM_CFLAGS ?= -O2 -DNDEBUG
 # The directory where we build the sysroot.
 SYSROOT ?= $(CURDIR)/sysroot
 # A directory to install to for "make install".
@@ -45,12 +45,10 @@ LIBC_BOTTOM_HALF_CLOUDLIBC_SRC_INC = $(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC)/include
 LIBC_BOTTOM_HALF_HEADERS_PUBLIC = $(LIBC_BOTTOM_HALF_DIR)/headers/public
 LIBC_BOTTOM_HALF_HEADERS_PRIVATE = $(LIBC_BOTTOM_HALF_DIR)/headers/private
 LIBC_BOTTOM_HALF_LIBPREOPEN_DIR = $(LIBC_BOTTOM_HALF_DIR)/libpreopen
-LIBC_BOTTOM_HALF_LIBPREOPEN_LIB = $(LIBC_BOTTOM_HALF_LIBPREOPEN_DIR)/lib
-LIBC_BOTTOM_HALF_LIBPREOPEN_INC = $(LIBC_BOTTOM_HALF_LIBPREOPEN_DIR)/include
 LIBC_BOTTOM_HALF_SOURCES = $(LIBC_BOTTOM_HALF_DIR)/sources
 LIBC_BOTTOM_HALF_ALL_SOURCES = \
     $(shell find $(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC) -name \*.c) \
-    $(LIBC_BOTTOM_HALF_LIBPREOPEN_LIB)/po_libc_wrappers.c \
+    $(LIBC_BOTTOM_HALF_LIBPREOPEN_DIR)/libpreopen.c \
     $(shell find $(LIBC_BOTTOM_HALF_SOURCES) -name \*.c)
 LIBWASI_EMULATED_MMAN_SOURCES = \
     $(shell find $(LIBC_BOTTOM_HALF_DIR)/mman -name \*.c)
@@ -364,9 +362,7 @@ $(DLMALLOC_OBJS): override WASM_CFLAGS += \
 startup_files $(LIBC_BOTTOM_HALF_ALL_OBJS): override WASM_CFLAGS += \
     -I$(LIBC_BOTTOM_HALF_HEADERS_PRIVATE) \
     -I$(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC_INC) \
-    -I$(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC) \
-    -I$(LIBC_BOTTOM_HALF_LIBPREOPEN_LIB) \
-    -I$(LIBC_BOTTOM_HALF_LIBPREOPEN_INC)
+    -I$(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC)
 
 $(LIBC_TOP_HALF_ALL_OBJS) $(MUSL_PRINTSCAN_LONG_DOUBLE_OBJS) $(MUSL_PRINTSCAN_NO_FLOATING_POINT_OBJS): override WASM_CFLAGS += \
     -I$(LIBC_TOP_HALF_MUSL_SRC_DIR)/include \

expected/wasm32-wasi/defined-symbols.txt

@@ -251,7 +251,6 @@ __uselocale
 __utc
 __wasilibc_fd_renumber
 __wasilibc_find_relpath
-__wasilibc_init_preopen
 __wasilibc_populate_environ
 __wasilibc_register_preopened_fd
 __wasilibc_rmdirat
@@ -428,7 +427,6 @@ drand48
 drem
 dremf
 duplocale
-eaccess
 ecvt
 encrypt
 environ

expected/wasm32-wasi/predefined-macros.txt

@@ -1143,6 +1143,7 @@
 #define NAN (0.0f/0.0f)
 #define NBBY 8
 #define NCARGS 131072
+#define NDEBUG 1
 #define ND_NA_FLAG_OVERRIDE 0x00000020
 #define ND_NA_FLAG_ROUTER 0x00000080
 #define ND_NA_FLAG_SOLICITED 0x00000040
@@ -3171,7 +3172,7 @@
 #define and_eq &=
 #define asin(x) __tg_real_complex(asin, (x))
 #define asinh(x) __tg_real_complex(asinh, (x))
-#define assert(x) ((void)((x) || (__assert_fail(#x, __FILE__, __LINE__, __func__),0)))
+#define assert(x) (void)0
 #define atan(x) __tg_real_complex(atan, (x))
 #define atan2(x,y) __tg_real_2(atan2, (x), (y))
 #define atanh(x) __tg_real_complex(atanh, (x))

libc-bottom-half/crt/crt1.c

@@ -11,8 +11,6 @@ extern void __prepare_for_exit(void);
 void _Exit(int) __attribute__((noreturn));
 
 static __wasi_errno_t populate_libpreopen(void) {
-    __wasilibc_init_preopen();
-
     // Skip stdin, stdout, and stderr, and count up until we reach an invalid
     // file descriptor.
     for (__wasi_fd_t fd = 3; fd != 0; ++fd) {