[llvm] Move sub-project lead maintainers into their own files

This adds Maintainers.md files to the sub-projects mentioned
here, so that someone going directly to that sub-project will
find them more easily.

Recently I needed to find a libclc maintainer and I had no
idea there was one listed here instead of in libclc/.

Author: DavidSpickett

libclc/Maintainers.md

@@ -0,0 +1,10 @@
+# libclc Maintainers
+
+This file is a list of the
+[maintainers](https://llvm.org/docs/DeveloperPolicy.html#maintainers) for
+libclc.
+
+# Lead maintainer
+
+Tom Stellard \
+[email protected] (email), [tstellar](https://github.com/tstellar) (GitHub)

llvm/Maintainers.md

@@ -422,7 +422,6 @@ [email protected] (email), [gkistanova](https://github.com/gkistanova) (GitHu
 ### Other subprojects
 
 Some subprojects maintain their own list of per-component maintainers.
-Others only have a lead maintainer listed here.
 
 [Bolt maintainers](https://github.com/llvm/llvm-project/blob/main/bolt/Maintainers.txt)
 
@@ -436,21 +435,15 @@ Others only have a lead maintainer listed here.
 
 [libc++ maintainers](https://github.com/llvm/llvm-project/blob/main/libcxx/Maintainers.md)
 
+[libclc maintainers](https://github.com/llvm/llvm-project/blob/main/libclc/Maintainers.md)
+
 [LLD maintainers](https://github.com/llvm/llvm-project/blob/main/lld/Maintainers.md)
 
 [LLDB maintainers](https://github.com/llvm/llvm-project/blob/main/lldb/Maintainers.rst)
 
 [LLVM OpenMP Library maintainers](https://github.com/llvm/llvm-project/blob/main/openmp/Maintainers.md)
 
-#### libclc
-
-Tom Stellard \
-[email protected] (email), [tstellar](https://github.com/tstellar) (GitHub)
-
-#### Polly
-
-Tobias Grosser \
-[email protected] (email), [tobiasgrosser](https://github.com/tobiasgrosser) (GitHub)
+[Polly maintainers](https://github.com/llvm/llvm-project/blob/main/polly/Maintainers.md)
 
 ## Inactive Maintainers
 

polly/Maintainers.md

@@ -0,0 +1,10 @@
+# Polly Maintainers
+
+This file is a list of the
+[maintainers](https://llvm.org/docs/DeveloperPolicy.html#maintainers) for
+Polly.
+
+# Lead maintainer
+
+Tobias Grosser \
+[email protected] (email), [tobiasgrosser](https://github.com/tobiasgrosser) (GitHub)