glibc version test feature

Author: vhscampos

libcxx/test/std/depr/depr.c.headers/uchar_h_char8_t.compile.pass.cpp

@@ -14,6 +14,7 @@
 // XFAIL: darwin
 // XFAIL: freebsd
 // XFAIL: windows
+// XFAIL: glibc-no-char8_t-support
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 
 // <uchar.h>

libcxx/test/std/strings/c.strings/cuchar_char8_t.compile.pass.cpp

@@ -14,6 +14,7 @@
 // XFAIL: darwin
 // XFAIL: freebsd
 // XFAIL: windows
+// XFAIL: glibc-no-char8_t-support
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 
 // <cuchar>

libcxx/utils/libcxx/test/features.py

@@ -293,6 +293,23 @@ def _mingwSupportsModules(cfg):
           """,
         ),
     ),
+    # Check for Glibc < 2.36, where there was no support for char8_t functions
+    Feature(
+        name="glibc-no-char8_t-support",
+        when=lambda cfg: "__GLIBC__" in compilerMacros(cfg)
+        and not sourceBuilds(
+            cfg,
+            """
+            #include <uchar.h>
+            #include <wchar.h>
+            int main(void) {
+                char8_t c;
+                mbstate_t s = {0};
+                return (mbrtoc8(&c, "", 0, &s), 0);
+            }
+            """,
+        ),
+    ),
     Feature(
         name="has-unix-headers",
         when=lambda cfg: sourceBuilds(