cmd/go/internal/load: use lowercase package directory comparisons on Windows
go build
command is short for
go build .
and it builds . package. When command above is executed from
directory inside of GOPATH, it uses GOPATH to calculate package
source directory. So . package uses GOPATH as part of package
source directory.
On the other hand
go build -ldflags=abc
only passes flag to the linker for packages that are listed
on the command line. The command above assumes . package again,
and that package source path is compared with current directory.
Current code compares result of os.Getwd with what GOPATH
environment variable contains. But these values might differ
in letter case on Windows. For example, one might return
c:\gopath\..., while the other might contain C:\GOPATH.