Define PLATFORM_GNU which covers any OS with GNU userland.

This define covers kFreeBSD, not just Linux. This is required because
the error which 120d194 works around is
a GNU problem, not a Linux problem, so causes FTBFS on kFreeBSD.

configure.ac

@@ -368,6 +368,7 @@ fi
 AC_SUBST(extra_runtime_ldflags)
 AM_CONDITIONAL(HOST_WIN32, test x$host_win32 = xyes)
 AM_CONDITIONAL(TARGET_WIN32, test x$target_win32 = xyes)
+AM_CONDITIONAL(PLATFORM_GNU, echo x$target_os | grep -q -- -gnu$)
 AM_CONDITIONAL(PLATFORM_LINUX, echo x$target_os | grep -q linux)
 AM_CONDITIONAL(PLATFORM_DARWIN, test x$platform_darwin = xyes)
 AM_CONDITIONAL(PLATFORM_SIGPOSIX, test x$use_sigposix = xyes)

mono/unit-tests/Makefile.am

@@ -11,7 +11,7 @@ endif
 if !CROSS_COMPILE
 if !HOST_WIN32
 if SUPPORT_BOEHM
-if !PLATFORM_LINUX
+if !PLATFORM_GNU
 
 test_sgen_qsort_SOURCES = test-sgen-qsort.c
 test_sgen_qsort_CFLAGS = $(TEST_CFLAGS)
@@ -37,7 +37,7 @@ noinst_PROGRAMS = test-sgen-qsort test-gc-memfuncs test-mono-linked-list-set tes
 
 TESTS = test-sgen-qsort test-gc-memfuncs test-mono-linked-list-set test-conc-hashtable
 
-endif !PLATFORM_LINUX
+endif !PLATFORM_GNU
 endif SUPPORT_BOEHM
 endif !HOST_WIN32
 endif !CROSS_COMPILE