build with musl

Skip libunwind support for musl-based Linux environments, and avoid
`__FLOAT_BITS`, etc., in xform.

racket/collects/compiler/private/xform.rkt

@@ -915,6 +915,7 @@
                __inline_isnanl __inline_isnan __inline_signbit __inline_signbitf __inline_signbitd __inline_signbitl
                __builtin_popcount __builtin_clz __builtin_isnan __builtin_isinf __builtin_signbit
                __builtin_signbitf __builtin_signbitd __builtin_signbitl __builtin_isinf_sign __builtin_trap
+               __FLOAT_BITS __DOUBLE_BITS
                _Generic
                __inline_isinff __inline_isinfl __inline_isinfd __inline_isnanf __inline_isnand __inline_isinf
                floor floorl ceil ceill round roundl fmod fmodl modf modfl fabs fabsl __maskrune _errno __errno

racket/src/cfg-racket

@@ -3419,6 +3419,7 @@ mzrt_needs_pthread=yes
 skip_iconv_check=no
 check_page_size=yes
 try_no_nullability_completeness=no
+check_for_unwind=no
 
 if test "${enable_cify}" = "yes" ; then
   STARTUP_AS_BYTECODE=_bytecode
@@ -4866,6 +4867,7 @@ case "$host_os" in
       x86_64)
        enable_parallel_by_default=yes
        CGC_X86_64="1"
+       check_for_unwind=REG_RSP
        ;;
       ppc|powerpc)
        ;;
@@ -4875,6 +4877,7 @@ case "$host_os" in
        ;;
       i386|i486|i586|i686)
        enable_parallel_by_default=yes
+       check_for_unwind=REG_ESP
        ;;
       arm*)
        EXTRA_GMP_OBJ="gmp_arm_gcc.o"
@@ -5795,6 +5798,35 @@ $as_echo "$can_mprotect_exec" >&6; }
   fi
 fi
 
+if test "${check_for_unwind}" != "no" ; then
+   msg="for unwind support"
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking $msg" >&5
+$as_echo_n "checking $msg... " >&6; }
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+     #include <inttypes.h>
+     #define __USE_GNU
+     #include <ucontext.h>
+     int main() {
+        return ${check_for_unwind};
+     }
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  can_unwind=yes
+else
+  can_unwind=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+  if test "$can_unwind" = "no" ; then
+
+$as_echo "#define MZ_NO_UNWIND_SUPPORT 1" >>confdefs.h
+
+  fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $can_unwind" >&5
+$as_echo "$can_unwind" >&6; }
+fi
+
 if test "${check_page_size}" = "yes" ; then
    msg="for large page size"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking $msg" >&5

racket/src/racket/configure.ac

@@ -305,6 +305,7 @@ mzrt_needs_pthread=yes
 skip_iconv_check=no
 check_page_size=yes
 try_no_nullability_completeness=no
+check_for_unwind=no
 
 if test "${enable_cify}" = "yes" ; then
   STARTUP_AS_BYTECODE=_bytecode
@@ -607,6 +608,7 @@ case "$host_os" in
       x86_64)
        enable_parallel_by_default=yes
        CGC_X86_64="1"
+       check_for_unwind=REG_RSP
        ;;
       ppc|powerpc)
        ;;
@@ -616,6 +618,7 @@ case "$host_os" in
        ;;
       i386|i486|i586|i686)
        enable_parallel_by_default=yes
+       check_for_unwind=REG_ESP
        ;;
       arm*)
        EXTRA_GMP_OBJ="gmp_arm_gcc.o"
@@ -955,6 +958,22 @@ if test "${check_for_mprotect}" = "yes" ; then
   fi
 fi
 
+if test "${check_for_unwind}" != "no" ; then
+  [ msg="for unwind support" ]
+  AC_MSG_CHECKING($msg)
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+     #include <inttypes.h>
+     #define __USE_GNU
+     #include <ucontext.h>
+     int main() {
+        return ${check_for_unwind};
+     }])], can_unwind=yes, can_unwind=no)
+  if test "$can_unwind" = "no" ; then
+    AC_DEFINE(MZ_NO_UNWIND_SUPPORT,1,[Missing ucontext support])
+  fi
+  AC_MSG_RESULT($can_unwind)
+fi
+
 if test "${check_page_size}" = "yes" ; then
   [ msg="for large page size" ]
   AC_MSG_CHECKING($msg)

racket/src/racket/mzconfig.h.in

@@ -95,4 +95,7 @@ typedef unsigned long uintptr_t;
 /* Use Generations with the GC */
 #undef USE_GC_GENS
 
+/* For platforms like Linux, where context info may not be available: */
+#undef MZ_NO_UNWIND_SUPPORT
+
 #endif

racket/src/racket/sconfig.h

@@ -147,12 +147,16 @@
 #if defined(__i386__)
 # define MZ_USE_JIT_I386
 # define MZ_JIT_USE_MPROTECT
-# define MZ_USE_DWARF_LIBUNWIND
+# ifndef MZ_NO_UNWIND_SUPPORT
+#  define MZ_USE_DWARF_LIBUNWIND
+# endif
 #endif
 #if defined(__x86_64__)
 # define MZ_USE_JIT_X86_64
 # define MZ_JIT_USE_MPROTECT
-# define MZ_USE_DWARF_LIBUNWIND
+# ifndef MZ_NO_UNWIND_SUPPORT
+#  define MZ_USE_DWARF_LIBUNWIND
+# endif
 #endif
 #if defined(__powerpc__) && !defined(__powerpc64__)
 # define MZ_USE_JIT_PPC