rtld: provide private getenv(3)

(cherry picked from commit b4b2748891)

libexec/rtld-elf/rtld-libc/Makefile.inc

@@ -27,7 +27,7 @@ SRCS+=	rtld_libc.c
 
 # Now build the remaining files from libc:
 .PATH: ${LIBC_SRCTOP}/stdlib
-SRCS+=	reallocf.c realpath.c getenv.c merge.c reallocarray.c
+SRCS+=	reallocf.c realpath.c merge.c reallocarray.c
 # TODO: fix merge.c to build with WARNS=6
 .if ${COMPILER_TYPE} == "clang"
 CFLAGS.merge.c+=-Wno-error=null-pointer-arithmetic

libexec/rtld-elf/rtld.c

@@ -6027,6 +6027,12 @@ rtld_strerror(int errnum)
 	return (sys_errlist[errnum]);
 }
 
+char *
+getenv(const char *name)
+{
+	return (rtld_get_env_val(environ, name, strlen(name)));
+}
+
 /* malloc */
 void *
 malloc(size_t nbytes)