Something

METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(Sy
** ERROR **: file class.c: line 2036 (mono_class_setup_vtable_general): should not be reached
aborting...
stem.Decimal)
METHOD op_Implicit(byte)
METHOD op_Implicit(sbyte)
METHOD op_Implicit(int16)
METHOD op_Implicit(uint16)
METHOD op_Implicit(char)
METHOD op_Implicit(int)
METHOD op_Implicit(uint)
METHOD op_Implicit(long)
METHOD op_Implicit(ulong)
METHOD op_Explicit(single)
METHOD op_Explicit(double)
METHOD op_Explicit(System.Decimal)
METHOD op_Explicit(System.Decimal)
METHOD op_Inequality(System.Decimal,System.Decimal)
METHOD op_Equality(System.Decimal,System.Decimal)
METHOD op_GreaterThan(System.Decimal,System.Decimal)
METHOD op_GreaterThanOrEqual(System.Decimal,System.Decimal)
METHOD op_LessThan(System.Decimal,System.Decimal)
METHOD op_LessThanOrEqual(System.Decimal,System.Decimal)

=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================

Stacktrace:

  at Mono.CSharp.CSharpParser.parse () <0xffffffff>
  at Mono.CSharp.CSharpParser.parse () <0x00067>
  at Mono.CSharp.Driver.parse (Mono.CSharp.SourceFile) <0x00163>
  at Mono.CSharp.Driver.ProcessFiles () <0x00059>
  at Mono.CSharp.Driver.MainDriver (string[]) <0x0038b>
  at Mono.CSharp.Driver.Main (string[]) <0x00045>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_int_string[] (object,intptr,intptr,intptr) <0xffffffff>

Native stacktrace:

        /var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mono/mini/mono(mono_handle_native_sigsegv+0xe4) [0x815b3f4]
        [0xffffe440]
        /lib/tls/libc.so.6(abort+0x18c) [0xb7d2615c]
        /usr/lib/libglib-2.0.so.0 [0xb7e96b55]
make[9]: *** [../../../class/lib/default/I18N.CJK.dll] Aborted
make[9]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs/class/I18N/CJK'
make[8]: *** [do-all] Error 2
make[8]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs/class/I18N/CJK'
make[7]: *** [all-recursive] Error 1
make[7]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs/class/I18N'
make[6]: *** [all-recursive] Error 1
make[6]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs/class'
make[5]: *** [all-recursive] Error 1
make[5]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs'
make[4]: *** [profile-do--default--all] Error 2
make[4]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs'
make[3]: *** [profiles-do--all] Error 2
make[3]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/mcs'
make[2]: *** [all-local] Error 2
make[2]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1/runtime'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/mono-1.1.16.1/work/mono-1.1.16.1'
make: *** [all] Error 2

!!! ERROR: dev-lang/mono-1.1.16.1 failed.
Call stack:
  ebuild.sh, line 1539:   Called dyn_compile
  ebuild.sh, line 939:   Called src_compile
  mono-1.1.16.1.ebuild, line 79:   Called die

!!! MONO compilation failure
!!! If you need support, post the topmost build error, and the call stack if relevant.