internal/build:compile with c mode,when c file

runtime/internal/lib/internal/cpu/_wrap/cpu_x86.c

@@ -1,6 +1,3 @@
-
-extern "C" {
-
 #if defined(__GNUC__) || defined(__clang__)
 void llgo_getcpuid(unsigned int eax, unsigned int ecx,
                    unsigned int *a, unsigned int *b,
@@ -22,5 +19,3 @@ void llgo_getcpuid(unsigned int eax, unsigned int ecx,
 #else
 #error This code requires GCC or Clang
 #endif
-
-}

runtime/internal/lib/internal/cpu/cpu_x86.go

@@ -10,7 +10,7 @@ import (
 
 const (
 	LLGoPackage = "link"
-	LLGoFiles   = "_wrap/cpu_x86.cpp"
+	LLGoFiles   = "_wrap/cpu_x86.c"
 )
 
 //go:linkname c_getcpuid C.llgo_getcpuid

runtime/internal/lib/internal/syscall/unix/_unix/fcntl_unix.c

@@ -9,8 +9,6 @@ struct fcntl_ret
     int32_t err; // Error code
 };
 
-extern "C" {
-
 // llgo_fcntl implements the fcntl system call wrapper for Go
 // fd: file descriptor
 // cmd: fcntl command
@@ -32,6 +30,4 @@ struct fcntl_ret llgo_fcntl2(int32_t fd, int32_t cmd, int32_t arg)
     }
 
     return ret;
-}
-
-}
+}

runtime/internal/lib/internal/syscall/unix/fcntl_unix.go

@@ -8,7 +8,7 @@ import (
 // llgo:skip fcntl
 const (
 	LLGoPackage = "link"
-	LLGoFiles   = "_unix/fcntl_unix.cpp"
+	LLGoFiles   = "_unix/fcntl_unix.c"
 )
 
 //go:linkname llgo_fcntl2 C.llgo_fcntl2

runtime/internal/lib/runtime/_wrap/runtime.c

@@ -1,7 +1,5 @@
 #include <unistd.h>
 
-extern "C" {
-
 int llgo_maxprocs()
 {
 #ifdef _SC_NPROCESSORS_ONLN
@@ -10,5 +8,3 @@ int llgo_maxprocs()
     return 1;
 #endif
 }
-
-}

runtime/internal/lib/runtime/runtime.go

@@ -28,7 +28,7 @@ type _runtime struct{}
 
 const (
 	LLGoPackage = "link"
-	LLGoFiles   = "_wrap/runtime.cpp"
+	LLGoFiles   = "_wrap/runtime.c"
 )
 
 // GOROOT returns the root of the Go tree. It uses the