Upgrade to 2.5.0-4 toolchain w/improved pgm_read_x, C++ exceptions (#6273)

* Upgrade to 2.5.0-4 toolchain w/improved pgm_read_x

Rebuild the entire toolchain (including standard libraries) with the
latest pgm_read_xxx headers included (which fix unaligned dword reads
from progmem and run faster/smaller, and a pgm_read_byte change which
removes an instruction on each read saving flash).

Pull in latest bearssl while we're at it, too, which speeds up EC
handshakes and reduced ROM usage, too.

* Fix C++ exceptions

Exception code now only does 32b aligned reads from progmem to access
the eh_table (some via -mforce-l32, some via hand-inserted pgm_read_x
macros).

Fixes #6151
Fixes #6305
Fixes #6198

Author: earlephilhower

package/package_esp8266com_index.template.json

@@ -1,2 +1,2 @@
 // Do not edit -- Automatically generated by tools/sdk/ssl/bearssl/Makefile
-#define BEARSSL_GIT 6b9587f
+#define BEARSSL_GIT 9247320