[gjs/master.msvc] README.MSVC.md: One more fix in the SpiderMonkey headers

[Chun-wei Fan <fanchunwei src gnome org>]

commit 97e47db92b9890139435cd1a347afbfca3bcfee6
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed Jul 7 18:36:14 2021 +0800

    README.MSVC.md: One more fix in the SpiderMonkey headers
    
    An extraneous JS_PUBLIC_API needs to be removed from the headers for GIT
    master to build.

 README.MSVC.md | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/README.MSVC.md b/README.MSVC.md
index 4145c571..3ea9a474 100644
--- a/README.MSVC.md
+++ b/README.MSVC.md
@@ -123,6 +123,13 @@ Get rid of the 'JS_FRIEND_API' macro from the class
 'TempAllocPolicy : public AllocPolicyBase' (ca. lines 112 and 178),
 for the member method definitions of onOutOfMemory() and reportAllocOverflow()
 
+-Update $(includedir)/mozjs-78/js/BigInt.h (after the build):
+
+Remove the 'JS_PUBLIC_API' macro from the definition of
+'template <typename NumericT>
+extern BigInt* NumberToBigInt(JSContext* cx, NumericT val)' (ca lines 72-73), as
+it should not be there.
+
 ======================
 To carry out the build
 ======================