Add support for multiple enumerator attributes

[lambdageek]

From GCC documentation on attribute syntax:

In GNU C, an attribute specifier list may appear as part of an enumerator. The attribute goes after the enumeration constant, before =, if present. The optional attribute in the enumerator appertains to the enumeration constant. It is not possible to place the attribute after the constant expression, if present.

where attribute specifier list is multiple attribute specifiers with no intervening tokens.

OSX /usr/include/time.h has multiple __attribute__((availability(...))) attributes stacked on each enumerator:

typedef enum {
_CLOCK_REALTIME __OSX_AVAILABLE(10.12) __IOS_AVAILABLE(10.0) __TVOS_AVAILABLE(10.0) __WATCHOS_AVAILABLE(3.0) = 0,
}

where __OSX_AVAILABLE(_vers) is __attribute__(((macosx,introduced=_vers))) and similarly for the others.