Fix double extern "C" pointed by clang.

Change-Id: Ie595dd99d01149868a4f60354ef89fa861cf856b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2389
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

src/system/libroot/posix/wchar/mbrtowc.cpp

@@ -85,5 +85,4 @@ __mbrtowc(wchar_t* pwc, const char* s, size_t n, mbstate_t* ps)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__mbrtowc, mbrtowc);

src/system/libroot/posix/wchar/mbsrtowcs.cpp

@@ -101,7 +101,6 @@ __mbsnrtowcs(wchar_t* dst, const char** src, size_t nmc, size_t len,
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__mbsnrtowcs, mbsnrtowcs);
 
 
@@ -119,5 +118,4 @@ __mbsrtowcs(wchar_t* dst, const char** src, size_t len, mbstate_t* ps)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__mbsrtowcs, mbsrtowcs);

src/system/libroot/posix/wchar/wcrtomb.cpp

@@ -75,5 +75,4 @@ __wcrtomb(char* s, wchar_t wc, mbstate_t* ps)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__wcrtomb, wcrtomb);

src/system/libroot/posix/wchar/wcscoll.cpp

@@ -28,5 +28,4 @@ __wcscoll(const wchar_t* wcs1, const wchar_t* wcs2)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__wcscoll, wcscoll);

src/system/libroot/posix/wchar/wcsrtombs.cpp

@@ -102,7 +102,6 @@ __wcsnrtombs(char* dst, const wchar_t** src, size_t nwc, size_t len,
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__wcsnrtombs, wcsnrtombs);
 
 
@@ -118,5 +117,4 @@ __wcsrtombs(char* dst, const wchar_t** src, size_t len, mbstate_t* ps)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__wcsrtombs, wcsrtombs);

src/system/libroot/posix/wchar/wcsxfrm.cpp

@@ -30,5 +30,4 @@ __wcsxfrm(wchar_t* dest, const wchar_t* src, size_t destSize)
 }
 
 
-extern "C"
 B_DEFINE_WEAK_ALIAS(__wcsxfrm, wcsxfrm);