BaseTools: Normalize case of pathname when evaluating Macros.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2880



Currently, When doing the Incremental build, the directory
macros extended to absolute path in output Makefile, which
is inconsistent with the output of Clean build.

When we do macro replacement, we can't replace macro due to
inconsistent path case, which results in inconsistent display
of incremental build and clean build in makefile.Therefore,
the path is converted to achieve the correct macro replacement.

Signed-off-by: Mingyue Liang <mingyuex.liang@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>

Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Yuwei Chen <yuwei.chen@intel.com>