fix(docs): make required compiler version == rather than >=

TF-A carries its own compiler-rt so higher versions of the compilers may
not necessarily work. Because TF-A is only tested on the specified
versions in the CI, any breakage remains unknown. Update the
prerequisites guide to make it more apparent that this is the case.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ia5da9c5ff505ead99f579f3f5fbe3a480d697c1d
diff --git a/docs/getting_started/prerequisites.rst b/docs/getting_started/prerequisites.rst
index 3723294..5b49d2e 100644
--- a/docs/getting_started/prerequisites.rst
+++ b/docs/getting_started/prerequisites.rst
@@ -31,12 +31,18 @@
    You will need the targets ``arm-none-eabi`` and ``aarch64-none-elf`` for
    AArch32 and AArch64 builds respectively.
 
-- Clang >= 14.0.0
-- Arm Compiler >= 6.18
+- Clang == 14.0.0
+- Arm Compiler == 6.18
 
 In addition, a native compiler is required to build the supporting tools.
 
 .. note::
+   Versions greater than the ones specified are likely but not guaranteed to
+   work. This is predominantly because TF-A carries its own copy of compiler-rt,
+   which may be older than the version expected by the compiler. Fixes and bug
+   reports are always welcome.
+
+.. note::
    The software has also been built on Windows 7 Enterprise SP1, using CMD.EXE,
    Cygwin, and Msys (MinGW) shells, using version 5.3.1 of the GNU toolchain.