src/est/est_locl.h: add missing extern on e_ctx_ssl_exdata_index

Without this extern, the variable gets re-declared in each compilation
unit including est_locl.h, causing gcc >= 10 to complain with:

/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_client.o:(.data+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_server.o:(.bss+0xc): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_server_http.o:(.bss+0x3b8): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_proxy.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_client_http.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_ossl_util.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_client_proxy.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_enhcd_cert_auth.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: .libs/est_server_coap.o:(.bss+0x0): multiple definition of `e_ctx_ssl_exdata_index'; .libs/est.o:(.bss+0x8): first defined here
collect2: error: ld returned 1 exit status

Signed-off-by: Thomas Petazzoni <[email protected]>

Author: tpetazzoni

src/est/est_locl.h

@@ -590,7 +590,7 @@ typedef struct est_oid_list {
 /*
  * Index used to link the EST Ctx into the SSL structures
  */
-int e_ctx_ssl_exdata_index;
+extern int e_ctx_ssl_exdata_index;
 
 LIBEST_TEST_API void est_log (EST_LOG_LEVEL lvl, char *format, ...);
 LIBEST_TEST_API void est_log_backtrace (void);