fix Issue 9720 - OSX wrong code with -O Illegal instruction
Improve 'is used as a type' template error

If a template instantiation fails, a spurious 'XXX is used as a type' error
is generated. Suppress it.
Also, when a constraint fails, change the instantiation error into a
supplemental error message.
fix Issue 9863 - Incorrect generation of SAHF instruction on 64 bits
clarify as suggested in pull #1813
Merge pull request #1827 from WalterBright/fix9863

fix Issue 9863 - Incorrect generation of SAHF instruction on 64 bits
Merge pull request #1823 from WalterBright/fix9720

fix Issue 9720 - OSX wrong code with -O Illegal instruction
add missing file sapply.c
Merge pull request #1819 from WalterBright/refactor

clarify as suggested in pull #1813
Merge pull request #1830 from rainers/fix_vsbuild4

fix build with Visual Studio
Merge pull request #1799 from donc/isusedasatype

Supress spurious 'is used as a type' template error message