Build on mipsel.

Backport new version to p9 branch.

New version (78.12.0).
Security fixes:
2021-29969 IMAP server responses sent by a MITM prior to STARTTLS could be processed
2021-29970 Use-after-free in accessibility features of a document
2021-30547 Out of bounds write in ANGLE
2021-29976 Memory safety bugs fixed in Thunderbird 78.12
Completely remove build external enigmail.

Backport new version to p9 branch.

New version (78.11.0).
Security fixes:
2021-29964 Out of bounds-read when parsing a `WM_COPYDATA` message
2021-29967 Memory safety bugs fixed in Thunderbird 78.11

Backport new version to p9 branch.

New version (78.10.2).
Security fixes:
2021-29957 Partial protection of inline OpenPGP message not indicated
2021-29956 Thunderbird stored OpenPGP secret keys without master password protection

Backport new version to p9 branch.

New version (78.10.1).
Security fixes:
2021-29951 Thunderbird Maintenance Service could have been started or stopped by domain users
Do not build for ppc64le.

New version (78.10.0).
Security fixes:
2021-23994 Out of bound write due to lazy initialization
2021-23995 Use-after-free in Responsive Design Mode
2021-23998 Secure Lock icon could have been spoofed
2021-23961 More internal network hosts could have been probed by a malicious webpage
2021-23999 Blob URLs may have been granted additional privileges
2021-24002 Arbitrary FTP command execution on FTP servers using an encoded URL
2021-29945 Incorrect size computation in WebAssembly JIT could lead to null-reads
2021-29946 Port blocking could be bypassed
2021-29948 Race condition when reading from disk while verifying signatures
2021-23991 An attacker may use Thunderbird's OpenPGP key refresh mechanism to poison an existing key
2021-23992 A crafted OpenPGP key with an invalid user ID could be used to confuse the user
2021-23993 Inability to send encrypted OpenPGP email after importing a crafted OpenPGP key
2021-29949 Thunderbird might execute an alternative OTR library
2021-23981 Texture upload into an unbound backing buffer resulted in an out-of-bound read
2021-23982 Internal network hosts could have been probed by a malicious webpage
2021-23984 Malicious extensions could have spoofed popup information
2021-23987 Memory safety bugs fixed in Thunderbird 78.9

New version (78.8.1).
Security fixes:
2021-29950 Logic issue potentially leaves key material unlocked

Backport new version to p9 branch.

New version (78.8.0).
Security fixes:
2021-23969 Content Security Policy violation report could have contained the destination of a redirect
2021-23968 Content Security Policy violation report could have contained the destination of a redirect
2021-23973 MediaError message property could have leaked information about cross-origin resources
2021-23978 Memory safety bugs fixed in Thunderbird 78.8

Backport new version to p9 branch.

New version (78.7.1).

Backport new version to p9 branch.