[compiler-rt] [test] Mark a windows specific test as requiring an MSVC like environment

This test relies on MSVC style linking details, such as -Wl,-dll
(which could be expressed with just "-shared", which would work
with MinGW too) and an implicitly created import library named
"<basename>.lib" (which isn't created when linking in MinGW mode).

This fixes running the compiler-rt tests in MinGW environments.

compiler-rt/test/profile/ContinuousSyncMode/online-merging-windows.c

@@ -1,4 +1,4 @@
-// REQUIRES: windows
+// REQUIRES: target={{.*windows-msvc.*}}
 
 // Test the online merging mode (%m) along with continuous mode (%c).
 //