Add .arm directives for the GLX entrypoint stubs.

Add .arm and .thumb directives before and after the ARMv7 GLX dispatch stubs.

The function addresses that get passed around don't take Thumb into account, so
if they're compiled as Thumb, then they'd still get executed as ARM, which
would cause them to crash a SIGILL.

src/GLX/glvnd_genentry.c

@@ -126,6 +126,10 @@ __asm__(".globl glx_entrypoint_start\n"
         ".balign " U_STRINGIFY(STUB_SIZE) "\n" \
         "glx_entrypoint_start:\n"
 
+#if defined(USE_ARMV7_ASM) && defined(__thumb__)
+        ".arm\n"
+#endif
+
 #define GLX_STUBS_ASM
 #include "g_glx_dispatch_stub_list.h"
 
@@ -133,6 +137,10 @@ __asm__(".globl glx_entrypoint_start\n"
         ".hidden glx_entrypoint_end\n"
         ".balign " U_STRINGIFY(STUB_SIZE) "\n" \
         "glx_entrypoint_end:\n"
+
+#if defined(USE_ARMV7_ASM) && defined(__thumb__)
+        ".thumb\n"
+#endif
 );
 
 static void *DefaultDispatchFunc(void)