fix static builds of zig from requiring c compiler

to be installed when linking libc.

When zig links against libc, it requires a dynamic linker path.
Usually this can be determined based on the architecture and operating
system components of the target. However on some systems this is not
correct; because of this zig checks its own dynamic linker.

When zig is statically linked, this information is not available, and so
it resorts to using cc -print-filename=foo to find the dynamic linker
path.

Before this commit, Zig incorrectly exited with an error if there was
no c compiler installed. Now, Zig falls back to the dynamic linker
determined based on the arch and os when no C compiler can be found.

src/codegen.cpp

@@ -8121,7 +8121,7 @@ static void detect_dynamic_linker(CodeGen *g) {
             for (size_t i = 0; possible_ld_names[i] != NULL; i += 1) {
                 const char *lib_name = possible_ld_names[i];
                 if ((err = zig_libc_cc_print_file_name(lib_name, result, false, true))) {
-                    if (err != ErrorCCompilerCannotFindFile) {
+                    if (err != ErrorCCompilerCannotFindFile && err != ErrorNoCCompilerInstalled) {
                         fprintf(stderr, "Unable to detect native dynamic linker: %s\n", err_str(err));
                         exit(1);
                     }

src/error.cpp

@@ -54,6 +54,7 @@ const char *err_str(Error err) {
         case ErrorOperationAborted: return "operation aborted";
         case ErrorBrokenPipe: return "broken pipe";
         case ErrorNoSpaceLeft: return "no space left";
+        case ErrorNoCCompilerInstalled: return "no C compiler installed";
     }
     return "(invalid error)";
 }

src/libc_installation.cpp

@@ -283,6 +283,8 @@ Error zig_libc_cc_print_file_name(const char *o_file, Buf *out, bool want_dirnam
     Buf *out_stdout = buf_alloc();
     Error err;
     if ((err = os_exec_process(cc_exe, args, &term, out_stderr, out_stdout))) {
+        if (err == ErrorFileNotFound)
+            return ErrorNoCCompilerInstalled;
         if (verbose) {
             fprintf(stderr, "unable to determine libc library path: executing '%s': %s\n", cc_exe, err_str(err));
         }

src/link.cpp

@@ -34,6 +34,7 @@ static CodeGen *create_child_codegen(CodeGen *parent_gen, Buf *root_src_path, Ou
     child_gen->verbose_cimport = parent_gen->verbose_cimport;
     child_gen->verbose_cc = parent_gen->verbose_cc;
     child_gen->llvm_argv = parent_gen->llvm_argv;
+    child_gen->dynamic_linker_path = parent_gen->dynamic_linker_path;
 
     codegen_set_strip(child_gen, parent_gen->strip_debug_symbols);
     child_gen->want_pic = parent_gen->have_pic ? WantPICEnabled : WantPICDisabled;

src/os.cpp

@@ -791,6 +791,7 @@ static Error os_exec_process_posix(const char *exe, ZigList<const char *> &args,
     int stdin_pipe[2];
     int stdout_pipe[2];
     int stderr_pipe[2];
+    int err_pipe[2];
 
     int err;
     if ((err = pipe(stdin_pipe)))
@@ -799,6 +800,8 @@ static Error os_exec_process_posix(const char *exe, ZigList<const char *> &args,
         zig_panic("pipe failed");
     if ((err = pipe(stderr_pipe)))
         zig_panic("pipe failed");
+    if ((err = pipe(err_pipe)))
+        zig_panic("pipe failed");
 
     pid_t pid = fork();
     if (pid == -1)
@@ -821,11 +824,12 @@ static Error os_exec_process_posix(const char *exe, ZigList<const char *> &args,
             argv[i + 1] = args.at(i);
         }
         execvp(exe, const_cast<char * const *>(argv));
+        Error report_err = ErrorUnexpected;
         if (errno == ENOENT) {
-            return ErrorFileNotFound;
-        } else {
-            zig_panic("execvp failed: %s", strerror(errno));
+            report_err = ErrorFileNotFound;
         }
+        write(err_pipe[1], &report_err, sizeof(Error));
+        exit(1);
     } else {
         // parent
         close(stdin_pipe[0]);
@@ -847,7 +851,13 @@ static Error os_exec_process_posix(const char *exe, ZigList<const char *> &args,
 
         if (err1) return err1;
         if (err2) return err2;
-        return ErrorNone;
+
+        Error child_err = ErrorNone;
+        write(err_pipe[1], &child_err, sizeof(Error));
+        close(err_pipe[1]);
+        read(err_pipe[0], &child_err, sizeof(Error));
+        close(err_pipe[0]);
+        return child_err;
     }
 }
 #endif

src/userland.h

@@ -56,6 +56,7 @@ enum Error {
     ErrorCacheUnavailable,
     ErrorPathTooLong,
     ErrorCCompilerCannotFindFile,
+    ErrorNoCCompilerInstalled,
     ErrorReadingDepFile,
     ErrorInvalidDepFile,
     ErrorMissingArchitecture,