truffle.nfi.native: detect musl in header file instead in suite definition

Author: lewurm

truffle/mx.truffle/suite.py

@@ -1034,12 +1034,6 @@
             "ldlibs" : ["-ldl"],
           },
         },
-        "linux-musl" : {
-          "<others>" : {
-            "cflags" : ["-g", "-O3", "-Wall", "-Werror", "-fvisibility=hidden"],
-            "ldlibs" : ["-ldl"],
-          },
-        },
         "<others>" : {
           "<others>" : {
             "cflags" : ["-g", "-O3", "-Wall", "-Werror", "-fvisibility=hidden"],

truffle/src/com.oracle.truffle.nfi.native/src/internal.h

@@ -41,11 +41,28 @@
 #ifndef __TRUFFLE_INTERNAL_H
 #define __TRUFFLE_INTERNAL_H
 
-#if defined(__linux__) && defined(_GNU_SOURCE)
+#if defined(__linux__)
+
+#if !defined(_GNU_SOURCE)
+#error "expected to be set via CLFAGS.  required for detection below"
+#endif
+
+/* musl does not set __USE_GNU in features.h
+ * source: https://stackoverflow.com/a/70211227
+ */
+#include <features.h>
+
+#ifdef __USE_GNU
+/* glibc */
 #define ENABLE_ISOLATED_NAMESPACE
 #define ISOLATED_NAMESPACE 0x10000
 #include <dlfcn.h>
-#endif
+
+#else  // !__USE_GNU
+/* musl. dlmopen not available */
+#endif // !__USE_GNU
+
+#endif // __linux__
 
 #include "native.h"
 #include "trufflenfi.h"