Basic: fix compilation with MSVC

MSVC doesn't like the instantiation of the structure in the initializer list.
Initialize it in the constructor body to repair the build.

TargetInfo.h(545) : error C2143: syntax error : missing ')' before '{'
TargetInfo.h(545) : error C2143: syntax error : missing ';' before '}'
TargetInfo.h(545) : error C2059: syntax error : ')'
TargetInfo.h(545) : error C2059: syntax error : ','
TargetInfo.h(547) : error C2143: syntax error : missing ';' before '{'
TargetInfo.h(547) : error C2447: '{' : missing function header (old-style formal list?)

llvm-svn: 225247