Fix stack use after scope in FcConfigCompareValue

Discovered by AddressSanitizer. When left_o and right_o are promoted the
promoted values are placed on the stack in FcValuePromotionBuffer.
The FcValuePromotionBuffers must then continue to be in scope while
left_o and right_o point into their content. In 9d4e5d0f the
FcValuePromotionBuffers were moved into the incorrect scope, leaving
left_o and right_o pointing into an object whose lifetime has ended.
This is similar to left and right which appear to have a smaller scope
but are actually required to be in the larger scope.

Correct this by moving the FcValuePromotionBuffers to the proper scope.
Leave the left and right FcValues where they are since they are in the
correct scope already.

This also adds to test-conf the ability to create charset, langset,
range, and matrix in patterns. This allows for a simple test which fails
under AddressSanitizer before this change and passes after.
3 files changed