Compilation: handle system C compiler not found

When linking libc and compiling natively, Zig tries to integrate with
the system C compiler. However, this caused Zig to fail when no system C
compiler is installed, despite the fact that Zig is perfectly capable of
compiling & linking libc without one.

This commit makes Zig fall back to using its own ability to provide libc
in the case that no C compiler is installed. For glibc, it means
sometimes getting the warning "zig cannot build new glibc version abc,
providing instead xyz".

Ideally, Zig would do some more validation about the system libraries
being linked against, and report an error in case it could not provide
the exact correct libc version of the system libraries (or that the
system libraries themselves conflict with each other), however, I think
it is fair to call that a separate enhancement.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/glibc.zig b/src/glibc.zig
index 4e33867169..3dd7565e96 100644
--- a/src/glibc.zig
+++ b/src/glibc.zig
@@ -719,17 +719,16 @@ pub fn buildSharedObjects(comp: *Compilation) !void {
                 .lt => continue,
                 .gt => {
                     // TODO Expose via compile error mechanism instead of log.
-                    log.err("invalid target glibc version: {}", .{target_version});
+                    log.warn("invalid target glibc version: {}", .{target_version});
                     return error.InvalidTargetGLibCVersion;
                 },
             }
-        } else {
+        } else blk: {
             const latest_index = metadata.all_versions.len - 1;
-            // TODO Expose via compile error mechanism instead of log.
-            log.err("zig does not yet provide glibc version {}, the max provided version is {}", .{
+            log.warn("zig cannot build new glibc version {}; providing instead {}", .{
                 target_version, metadata.all_versions[latest_index],
             });
-            return error.InvalidTargetGLibCVersion;
+            break :blk latest_index;
         };
 
         {