Update and comment BoringSSL prefix hacks

templates/src/objective-c/BoringSSL-GRPC.podspec.template

@@ -223,13 +223,18 @@
       % endfor
       EOF
 
-      # Remove lines of the format "#define SOME_MACRO SOME_MACRO" because they mess up the symbol prefix
+      # The symbol prefixing mechanism is performed by redefining BoringSSL symbols with
+      # "#define SOME_BORINGSSL_SYMBOL GRPC_SHADOW_SOME_BORINGSSL_SYMBOL". Unfortunately, some symbols are already
+      # redefined as macros in BoringSSL headers in the form "#define SOME_BORINGSSL_SYMBOL SOME_BORINGSSL_SYMBOL"
+      # Such type of redefinition will cause "duplicate symbols" when using together with our prefix header. So
+      # the workaround in the below lines removes all such type of #define directives.
       sed -i'.back' '/^#define \\([A-Za-z0-9_]*\\) \\1/d' include/openssl/*.h
-      # Remove lines of the format below because they mess up the symbol prefix
-      #     #define SOME_MACRO ${"\\"}
-      #         SOME_MACRO
+      # Remove lines of the format below for the same reason above
+      #     #define SOME_BORINGSSL_SYMBOL ${"\\"}
+      #         SOME_BORINGSSL_SYMBOL
       sed -i'.back' '/^#define.*\\\\$/{N;/^#define \\([A-Za-z0-9_]*\\) *\\\\\\n *\\1/d;}' include/openssl/*.h
-      sed -i'.back' 's/#ifndef md5_block_data_order/#ifndef GRPC_SHADOW_md5_block_data_order/g' crypto/fipsmodule/md5/md5.c
+
+      # We are renaming openssl to openssl_grpc so that there is no conflict with openssl if it exists
       find . -type f \\( -path '*.h' -or -path '*.cc' -or -path '*.c' \\) -print0 | xargs -0 -L1 sed -E -i'.grpc_back' 's;#include <openssl/;#include <openssl_grpc/;g'
     END_OF_COMMAND