Correct access permissions to include "user execute" for run-msbuild.sh. (#13042)

Correct access permissions to include "user execute" for run-msbuild.sh. (#13042)

Correct access permissions for run-msbuild.sh.  Adding "user execute" seems to fix the following build error.  With this change I'm able to build on windows in Cygwin.  without, I see the below error:

```
$ make -j4
(CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /cygdrive/c/mono/mono/missing autoheader)
rm -f stamp-h1
touch config.h.in
cd . && /bin/sh ./config.status config.h
config.status: creating config.h
config.status: config.h is unchanged
Git submodules updated successfully
make  all-recursive
make[1]: Entering directory '/cygdrive/c/mono/mono'
Making all in msvc
make[2]: Entering directory '/cygdrive/c/mono/mono/msvc'
Building Mono runtime using Visual Studio.
../msvc/run-msbuild.sh "build" "i686"
**/bin/sh: ../msvc/run-msbuild.sh: Permission denied**
make[2]: *** [Makefile:614: all-local] Error 126
make[2]: Leaving directory '/cygdrive/c/mono/mono/msvc'
make[1]: *** [Makefile:583: all-recursive] Error 1
make[1]: Leaving directory '/cygdrive/c/mono/mono'
make: *** [Makefile:513: all] Error 2
```

(cherry picked from commit fe7c3d43e5c40a5918223ae4ef2189ffb275c4ae)